HomeMy WebLinkAbout5D Public Works Design Manual Updates
Phone 952.447.9800 / Fax 952.447.4245 / www.cityofpriorlake.com
4646 Dakota Street SE
Prior Lake, MN 55372
CITY COUNCIL AGENDA REPORT
MEETING DATE: JUNE 13, 2016
AGENDA #: 5D
PREPARED BY: PETE YOUNG, WATER RESOURCES ENGINEER
PRESENTED BY: PETE YOUNG
AGENDA ITEM: CONSIDER APPROVAL OF A RESOLUTION APPROVING CHANGES IN
THE CITY PUBLIC WORKS DESIGN MANUAL WITH RESPECT TO
HYDROLOGY
DISCUSSION: Introduction
The purpose of this item is to consider proposed updates to the Hydrology
section of the City’s Public Works Design Manual (PWDM), including
associated figures and exhibits.
History
The PWDM provides a standard for developers, builders, and their
engineers as well as City staff for use in design, construction, and
connection to public infrastructure facilities within the City The manual has
been refined by City staff over the years and is subject to change from time
to time as technology and state/federal rules are updated. The PWDM is
referenced as standard in both the subdivision ordinance and the standard
development contract.
The City Council passed Resolution 96-21 approving the original PWDM on
February 20, 1996. Subsequent updates were approved in 2002, 2006, and
2007. Since the most recent update, changes in technology and certain
state requirements relating to stormwater have occurred.
Updating the Hydrology section of the PWDM is part of an overall strategy
to ensure that the City remains compliant with state stormwater permit and
requirements. State stormwater rules now require explicit permit language
to be included in local rules documents such as the PWDM. Additional
updates to other documents are anticipated, including the Stormwater
ordinance and the Local Surface Water Management Plan (LSWMP).
Current Circumstances
The Hydrology section of the PWDM requires an update due to recent
changes to state stormwater requirements. The City must comply with these
changes according to our existing Municipal Separate Storm Sewer System
(MS4) permit. The Hydrology section of the PWDM contains equivalent
stormwater rules to both the Prior Lake-Spring Lake Watershed District
(PLSLWD) and the Scott Water Management Organization (WMO) and
updates to the PWDM will not jeopardize this equivalency. These agencies
have also recently updated their rules to comply with MS4 requirements.
2
A copy of the PWDM is attached to this agenda report, along with a guide to
the proposed changes and a fact sheet on MS4 requirements.
Conclusion
Staff recommends updating the PWDM to ensure compliance with our MS4
permit and state stormwater requirements. The proposed updates have
been reviewed by the City attorney. The proposed updates will ensure
continued compliance with state standards and incorporate changes to
standard engineering practices made since 2007. The proposed PWDM
changes will not significantly alter the requirements for development or
redevelopment within the City because developers must already comply
with the existing state requirements.
ISSUES: The proposed changes to the PWDM are summarized in Attachment 1 and
include:
1. Incorporated state MS4 requirements throughout the document.
2. Updated standard storm precipitation depths and rainfall distribution to
the current industry-engineering standard (Atlas 14 precipitation data and
MSE3 rainfall distribution).
3. Updated rate control standards to the current industry-engineering
standard and to be consistent with other local cities (including Savage and
Shakopee), PLSLWD, Scott County, Scott WMO, and MnDOT.
4. Minor updates to Exhibits L, O, and Q and Figures 1 and 2 (outlined in
Attachments 4-8).
5. Minor wording changes, clarifications, and definitions.
FINANCIAL
IMPACT:
Updating City standards and clarifying requirements will reduce confusion
for developers and City staff review time. Any increase in cost to developers
(for implementation) or to the City (for long -term operation and
maintenance) is due to the updated MS4 requirements.
ALTERNATIVES: 1. Motion and second as part of the consent agenda to approve a
resolution to approve the updates to the Hydrology section of the
PWDM and associated figures and exhibits.
2. Remove this item from the consent agenda for discussion.
RECOMMENDED
MOTION:
Alternative 1.
4646 Dakota Street SE
Prior Lake, MN 55372
RESOLUTION 16-XXX
A RESOLUTION APPROVING CHANGES IN THE CITY PUBLIC WORKS DESIGN MANUAL
WITH RESPECT TO HYDROLOGY
Motion By: Second By:
WHEREAS, The City Council passed resolution 96-21approving the Public Works Design
Manual; and,
WHEREAS,
WHEREAS,
This manual must be updated from time to time due to changes in state
requirements, standard engineering practices, and technology; and,
The City Council will review the Public Works Design Manual periodically.
NOW THEREFORE, BE IT HEREBY RESOLVED BY THE CITY COUNCIL OF PRIOR LAKE,
MINNESOTA as follows:
1. The recitals set forth above are incorporated herein.
2. The revised Public Works Design Manual is hereby adopted.
PASSED AND ADOPTED THIS 13th DAY OF JUNE 2016.
VOTE Hedberg Keeney McGuire Morton Thompson
Aye ☐ ☐ ☐ ☐ ☐
Nay ☐ ☐ ☐ ☐ ☐
Abstain ☐ ☐ ☐ ☐ ☐
Absent ☐ ☐ ☐ ☐ ☐
______________________________
Frank Boyles, City Manager
Summary of Proposed Updates
Amendment to the PWDM, Part III – Hydrology Rules
Section Update Summary Comments
Overall Amendment to PWDM None of the proposed changes will
jeopardize the City’s rules equivalency
agreements with Scott WMO and
PLSLWD
Overall Changed all references to specific city job titles and city
departments to “City”
Per comments from City attorney
Introductory Text Minor wording changes Clarification
1 – Definitions Minor wording changes Clarification
1 – Definitions Added definitions for state MS4 & Construction Stormwater
permits
Needed for references to state permits; in
general, state permits now require
specific language to be contained within
local rules documents such as the PWDM
1 – Definitions Deleted definition for “Volume Abstraction” This term is not used in the document
2 – Format & Standards Minor wording changes Clarification
2 – Format & Standards Removed the requirement to pave access routes to stormwater
infrastructure
This change has already been made in
practice and does not impact long-term
maintenance effectiveness
2 – Format & Standards Added list of elements required for a stormwater management
plan
It appears these elements were meant to
be included but did not make it into the
final adopted PWDM document
3 – Grading & ESC Clarified land disturbance thresholds, no change to actual
requirements or thresholds
For consistency with state rules
3 – Grading & ESC Deleted the provision that sites disturbing over 10,000 sf in
shoreland must apply for NPDES permit coverage
City cannot require State permit coverage
for sites <1 ac; however, SWPPP must
still be prepared for these sites
4 – Hydrology Minor wording changes Clarification
4 – Hydrology Added term “Qualifying Small Sites” Describes sites that require rate and
volume control, but disturb <1 ac. City
minimum thresholds not changed.
4 – Hydrology Updated standard storm precipitation depths and rainfall
distribution. Minimal change for 2-yr and 10-yr storm events.
100-yr storm event changing from 6.0 inches to 7.39 inches.
Atlas 14 precipitation data and the NRCS
MSE3 rainfall distribution are the new
engineering standards being used
throughout Minnesota; updated
throughout the document
ATTACHMENT 1
4 – Hydrology Updated rate control standards. Standard requirements would
now be equivalent to industry standard and will result in less
restrictive rate control requirements than current city rules
stipulate. However, more restrictive standards would still apply
to areas tributary to the Prior Lake Outlet Channel, where
flooding and capacity both need to be closely monitored and
restricted. Other areas do not have a demonstrated need for a
non-standard rate control restriction.
Changed to be consistent with the rate
control requirements used by adjacent
cities (Savage, Shakopee), PLSLWD,
Scott County, Scott WMO, and MnDOT.
Basic requirement is to match pre- and
post-development runoff rates for critical
storm events.
4 – Hydrology Clarified volume control standards and added State permit
requirement references
No change to existing volume control
requirements for small sites; added new
State requirements for clarification; no
new restrictions, but MS4 permit requires
state language to be contained within
local rules documents such as the PWDM
5 – Drainage/Floodplain No proposed changes n/a
6 – Wetlands Minor wording changes Clarification
6 – Wetlands Removed reference to specific MnRAM version MnRAM is updated frequently and the
current version will apply
6 – Wetlands Added reference to standard City plate for wetland buffer signs Removed long section of descriptive text
that is already listed on City Plate #203
7 – Pond Design Minor wording changes Clarification
8 – Storm Sewer Design Minor wording changes Clarification
9 – Misc. & Credits Minor wording changes Clarification
9 – Misc. & Credits Added requirement that “other methods” of natural area
preservation denotation must be approved by the City
Clarification; already done in practice
9 – Misc. & Credits Modified soil amendment requirements. Previous requirements
were in conflict: soil amendments only allowed from the back of
the building to the rear lot limit, then front and side areas were
mentioned in the next sentence.
Clarifies requirements and will result in
all soil amendments being accomplished
at one time, resulting in a better outcome
and simplifying the process
Exhibits L, O, Q Modified PWDM Exhibits L, O, and Q Minor wording changes for Exhibit L
relating to erosion and sediment control
terminology; Exhibit O is a new SWPPP
template from the MPCA that replaces
their old template; Exhibit Q outlines the
City’s protocol for administration of the
Wetland Conservation Act (WCA).
Slight changes to state WCA program
since last PWDM revision in 2007.
Figures 1, 2 Modified Figures 1 and 2 Updates to maps showing current city
and watershed boundaries; minor updates
since last PWDM revision in 2007
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
1
PART III
HYDROLOGY RULES
Site hydrology must follow the rules specified herein. These rules are based on the policiesy set forth
in the City of Prior Lake Local Surface Water Management Plan (LSWMP), the Water Resource
Management Plan of the Prior Lake- Spring Lake Watershed District (PLSLWD), and the
Comprehensive Water Resource Management Plan and Rules of the Scott Water Management
Organization (Scott WMO).
By enforcing the rules spelled out in rules of this Ppart, III the City of Prior Lake is fulfilling the
requirements spelled out underof State Statute Chapters 103B, and 103D, and Minnesota Rules
Chapter 8410. The City of Prior Lake enforces these rules under the terms spelled out inof a
Memorandum of Understanding or Memorandum of Agreement (MOU or MOA) with both the
PLSLWD and Scott WMO.
In the future, when major amendments are needed in this pPart III, the Scott WMO Board and the
PLSLWD Board must be consulted and must grant approval for said amendments as required by the
Scott WMO, PLSLWD, State Statute, and Minnesota Rules.
Index of Sections
Section One Definitions
Section Two Format and Standards
Section Three Grading, Erosions and Sediment Control
Section Four Site Hydrology and Stormwater and Volume Management
Section Five Drainage Alterations and Floodplain Management
Section Six Wetlands
Section Seven Pond Design Criteria
Section Eight Storm sSewer Design Criteria
Section Nine Miscellaneous and CN Reductions
SECTION ONE:
DEFINITIONS
Best Management Practices (BMPs): Techniques that are proven to be effective in the management
of stormwater, including those documented in the Minnesota Stormwater Manual (MPCA, 2005),
Protecting Water Quality in Urban Areas (MPCA 2000), and others as amended. Practices to prevent
or reduce the pollution of the waters of the state, including schedules of activities, prohibition of
practices, and other management practices, and also includes treatment, requirements, and
operating procedures and practices to control plant site runoff, spillage or leaks, sludge, or waste
disposal or drainage from raw material storage. BMPs include practices documented in the Minnesota
Stormwater Manual (MPCA), Protecting Water Quality in Urban Areas (MPCA, 2000), and other
MPCA manuals, alls as amended.
Buffer: An area of natural, non-invasive, permanently undisturbed, vegetated ground cover adjoining
and surrounding a wetland measured from the delineated edge of the wetland.
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Public Works Design Manual
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Buffer Averaging: Varying the width of a buffer while maintaining compliance with all buffer
requirements outlined in Section Six, Wetlands. A buffer of variable width around a wetland may have
variable width as long as any minimum buffer width requirements are met. The overall buffer area
must be equal in area to a corresponding fixed width buffer around the same wetland, set at the
average width.
Common Plan of Development or Sale: A contiguous area where multiple separate and distinct land
disturbing activities may be taking place at different times, on different schedules, but under one
proposed plan. One plan is broadly defined to included design, permit application, advertisement or
physical demarcation indicating that land disturbing activities may occur.
Construction Activity: A disturbance to the land that results in a change in the topography, existing
soil cover (both vegetative and non-vegetative), or the existing soil topography that may result in
accelerated stormwater runoff, leading to soil erosion and movement of sediment into surface waters
or drainage systems. Examples of construction activity may include clearing, grading, filling, and
excavating.
EOF: Emergency Overflow.
Expandable Ponding: Ponds built in low areas common to multiple developments that can be easily
expanded when neighboring areas develop.
HWL: 100-yr High water level of a pond or basin resulting from the 100-year, 24-hour storm.
Landlocked Basin: Any depression with a contributing drainage area greater than 1 acre that does
not have a natural surface outflow below the level of the 100- year, 24-hour storm, or below its OHW.
LSWMP: Local Surface Water Management Plan.
Maintained Area: Turf grass or landscaped area that receives regular maintenance such as mowing
or mulching.
MS4 Permit: MPCA General Permit authorizing the discharge of stormwater associated with small
Municipal Separate Storm Sewer Systems (MS4) under the NPDES/SDS permit program; Permit No.
MNR040000.
Net Acre: Total land area minus any wetland, lake, or bluff acreage.
New Development: All construction activity that is not defined as redevelopment.
No-grade zone: An area around a wetland that where no change in grade is allowed.
NPDES Construction Stormwater Permit: MPCA General Permit authorizing the discharge of
stormwater associated with construction activity under the NPDES/SDS Program; Permit No.
MNR100001.
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
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NWL: Normal water level, the elevation of the permanent wet pool of for a pond or basin.
OE: Outlet Eelevation, the primary outlet elevation of a pond or basin.
OHW : Ordinary High Water level.
Qualifying Small Sites: Sites where development, redevelopment, or change in use creates more
than 3,500 square feet of new impervious area and disturbs more than 10,000 square feet of land,
but where coverage under the NPDES Construction Stormwater Permit is not required.
Redevelopment: Any construction activity where, prior to the start of construction, the areas to be
disturbed have 15 percent or more of impervious surface(s).
Reduce: Reduce to the Maximum Extent Practicable (MEP) unless otherwise defined in the context
in which it is used.
Regional ponding: Permanent stormwater facility used to provide rate control and water quality
treatment for an area that encompasses two or more entities (including but not limited to;
developments, subdivisions, building additions, and conditional uses.).
Stormwater: Stormwater runoff, snow melt runoff, and surface runoff and drainage.
Stormwater Management Overlay District: An area within the City that has a separate set of
standards, generally defined by a tributary feature. (Example; : Any area draining to the Prior Lake
Outlet Channel).
Structural Stormwater BMP: A stationary and permanent BMP that is designed, constructed, and
operated to prevent or reduce the discharge of pollutants in stormwater.
Swale: A wide, shallow, vegetated depression in the ground designed to channel drainage of water.
Tributary Acrea: Total land area that drains intotributary to a pond, wetland, ditch, stream, reach, or
other point of interest on site in the existing condition, prior to any drainage alterations or landlocked
basin connections.
Volume Abstraction: Policy of encouraging infiltration, evaporation and transpiration to mitigate the
volume increasing effects of urbanization.
Volume Management: Policy of lLimiting volume and rate of stormwater entering lakes a receiving
water by impounding water for extended durations within the upper reaches of the Tributary in
stormwater ponds and wetlands aits tributary area. to mitigate the increased water volume effects of
urbanization on the watershed.
Volume Storage: Volume set aside for holding stormwater below a natural or created outfall that
during hydrologic variation mitigates effects of increased stormwater volume.
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
4
SECTION TWO:
FORMAT AND STANDARDS
2.1 Construction Drawings
Show the OE and HWL for ponds and the OHW for water bodies on the plans.
Show garage floor, low floor, and rear pad elevations and housing style for each unit on the grading
plan. Include a schematic describing each housing style and typical grading.
Show limits of clearing and limits of grading on grading plan and tree preservation plan. Show removal
of all trees and brush that will occur below the controlled water levelNWL that will be impacted fromof
existing and newly created ponding areas.
Show emergency overflow routes using arrows from all low points and show elevation of high point
along emergency overflow route. All emergency overflow routes shall be graded and the easement
area sodded prior to Building Permit issuance.
Show or define access routes for maintenance purposes to all inlets or outlets atstormwater
infrastructure and ponding areas (must be maximum of 8% grade, maximum of 2% cross slope, and
minimum of 10’ wide). Drainage and utility easements shall be dedicated at the time of final platting
to provide this access. Paving or pavers on the access routes is required with a design load to able
support maintenance vehicles.
2.2 Stormwater Management Report
Calculations shall be submitted showing proposed design elements that meet requirements spelled
out in of this AppendixPart. A narrative describing the proposed system shall accompany this
collection of calculations. The stormwater narrative shall be a brief and clear description of the
stormwater system that summarizes and reference figures, tables and plan sheets. The following are
the minimum summary/narrative elements:
Narrative describing the proposed system, referencing requirements in this Part
Summary of existing and proposed offsite runoff rates and volumes
Summary of volume control requirements and curve number reductions claimed
Narrative describing volume control method and why it was chosen
Summary of volume control system showing that it meets requirements
Existing and proposed drainage maps
Walker method calculations
SECTION THREE:
GRADING, EROSION AND SEDIMENT CONTROL
Site Eerosion and Ssediment Ccontrol described here is in addition to augments the Stormwater
Pollution Prevention Plan (SWPPP) as required by the MPCA’s NPDES General Permit to Discharge
Stormwater Associated with Construction Site Activity under the NPDES/SDS ProgramPermit
(NPDES Construction Stormwater Permit). All sites must comply with the NPDES Construction
Stormwater Permit regardless of whether the builder/developer is party to th e PermitEven when not
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
5
party to a NPDES Construction Stormwater Permit the City of Prior Lake remains involved and serves
as a monitor to confirm that the NPDES Construction Site Stormwater Permit is being followed.
3.1 Grading Standards
Maximum 4:1 slopes are allowed in “maintained” areas except approved by the City Engineer.
Maximum 3:1 slopes are allowed for road fill sections adjacent to water bodies, buffers, or natural
resource preservationother areas permanently protected by easements or City ownership.
Minimum grade for drainage swales and lot grading shall be 2% or greater. Drainage swales shall
have a Mmaximum length of the greater of: for drainage swales shall be(i) 300 feet; (ii) or a total of
eight lots draining to a point; or (iii), or as approved by the City Engineer. Backyard drainage
structures should be avoided. Drainage swales shall be graded and stabilized (drainage blanket,
seed and mulch, or sod) prior to the issuance of Building Permits.
A minimum of 15 feet beyond the house pad shall have a slope less than 10:1.
Show or define paved access routes for maintenance purposes to all manholes outside the public
right-of-way and inlets or outlets at ponding areas (8% maximum grade, 2% cross slope, and 10’
wide). Access easements shall be dedicated at the time of final platting to provide this access.
Verify locations and design of all overland drainage routes for capacity and erosion potential. All low
points in streets must have E.O.F’s designed for the 100 year storm event.
3.2 Erosion and Sediment Control / SWPPP Standards.
All development construction activity that disturbs results in land disturbance of equal to or greater
than 1 acre (or 10,000 sf in a shoreland) or a common plan of development or sale that disturbs
greater than 1 acre area must apply for and comply with the requirements of a the NPDES
Cconstructions site Stormwater NPDES Permit. The SWPPP must be reviewed and approved by the
City before an Excavating and Grading Permit is issued.
An SWPPP that meets the requirements of the NPDES Construction Stormwater Permit must be
prepared for aAll construction activity that results in land disturbance of equal to or greater than
10,000 square feet in a shoreland zone must prepare a SWPPP that meets the requirements of the
NPDES Construction Stormwater Permit. The SWPPP must be reviewed and approved by the City
before an Excavating and Grading Permit is issued.
All provisions of a the NPDES Constructions Site Stormwater Permit & SWPPP must be adhered to
for the duration of the City grading permit.
Provide name of company, contact person, and phone number for person responsible for erosion and
sediment control planSWPPP preparation, implementation, and maintenance.
Provide a note on the plans specifying that all down gradient erosion sediment control best
management practicesBMPs shall be installed by the Contractor and inspected by the City prior to
any site land disturbancework. The City must inspect and approve these BMPs before land
disturbance may occur.
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
6
Slopes greater than or equal to 4:1 shall have erosion control blanket installed immediately after
finished grading.
Areas coming out of agricultural production must be seeded with a cover crop prior to development.
SECTION FOUR:
SITE HYDROLOGY, STORMWATER AND VOLUME MANAGEMENT
4.1 General Standards
A hydrologic method, based on sound hydrologic theory must be used to analyze runoff for the design
of stormwater conveyance systems and permanent stormwater facilities. Curve numbers shall follow
recommendations of SCS Technical Release 55, Second Edition (TR-55, 1986).
Rate and volume control will be required for all development, redevelopment, or change in use that
creates more than 3,500 SF square feet of new impervious area and disturbs more than 10,000 SF
square feet of land. Sites exceeding these thresholds that do not require coverage under the NPDES
Construction Stormwater Permit are termed Qualifying Small Sites.
4.2 Rate Control
NOAA Atlas 14 precipitation depths resulting from the 2-, 10- and 100- year, 24-hour (24hour NRCS
Type II) storm events (NRCS MSE3 rainfall distribution) shall be modeled for existing and proposed
conditions. Events NOAA Atlas 14 precipitation depths for Prior Lake are 2.84”, 4.22” and 6.07.39”
for the 2-, 10- and 100- year, 24-hour storm events, respectively. (See Section 1, Definitions for
italicized terms)
Rate Control Standard:
Discharge Rrates control for the 2-, 10-, and 100-year, 24-hour storm events existing before the
proposed development, redevelopment, or change in use shall hold total offsite peak runoff at or
below the following schedule:not be increased.
2 year: 0.05 cfs per net acre
10 year: 0.30 cfs per net acre
100 year: Existing peak flow
Stormwater Management Overlay District #1 – Prior Lake Outlet Channel: (Figure 1)
Rate control for areas tributary areas to the Prior Lake oOutlet cChannel shall hold total offsite peak
runoff at or below the following schedule:
2- year, 24-hour event: 0.25 cfs per net acre
10- year, 24-hour event: 0.25 cfs per net acre
100- year, 24-hour event: 0.25 cfs per net acre
Alternate Rate Control Standard for Wetlands Utilized for Volume Management:
A portion of the 10- and 100- year, 24-hour storm events from a development may utilize wetlands
for stormwater rate control. The wetland must be eligible based on the requirements of Section 6Six,
Wetlands. The following schedule shall apply to the rate control a wetland provides.
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
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The Alternate Standard for Wetlands shall hold discharge out of a utilized wetland at or below the
following rate schedule:
2 year: 0.05 cfs per tributary acre
10 year: 0.15 cfs per tributary acre *
100 year: Existing peak flow *
* May be overridden by a stormwater management overlay district.
* In the case that the wetland cannot provide the volume for active storage in the 10- and 100- year
storms, the upstream stormwater system must be sized such that the system meets this requirement.
Any proposed improvements utilizing wetlands for portions of the 10- or 100- year event storage must
consider the build out condition of the watershed draining to that wetland. Developments will be
allowed to utilize a wetland proportional to their share of the tributary area. Rate control must be
constructed to serve the build-out condition of the entire subwatershed based on current zoning.
Information on the utilization of wetlands for volume storage can be found in Section 6 of this
appendixPart. Wetlands may not be eligible for utilization if land ownership or easements for
stormwater uses cannot be obtained.
Additional requirements for rate control may be set by the Engineering DivisionCity. The utilization
of wetlands for active storage or volume storage is subject tomay only be done with the approval of
the Engineering DivisionCity.
4.3 Volume Control
Volume Control Standard 1 – Qualifying Small Sites:
Applies to qualifying small sites as defined in this Section. In an effort to mitigate the effects of
increased volume discharged from urbanization, sSite runoff volume for qualifying small sites shall
be reduced in the proposedfrom pre-project conditions by a volume equal to or greater than 0.5 inch
per _______over all new impervious surfaces, unless that standard is modified by a Stormwater
Management Overlay District.
Volume Control Standard 2 – NPDES Permit Sites:
Applies to new development and redevelopment projects with land disturbance of greater than or
equal to 1 acre, including projects less than 1 acre that are part of a larger common plan of
development or sale and that discharge to the Prior Lake MS4.
For new development projects, site runoff shall have no net increase from pre-project conditions (on
an annual average basis) of:
Stormwater discharge volume (unless precluded by stormwater management limitations listed
in this Section)
Stormwater discharge of Total Suspended Solids (TSS)
Stormwater discharge of Total Phosphorus (TP)
For redevelopment projects, site runoff shall have a net reduction from pre-project conditions (on an
annual average basis) of:
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
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Stormwater discharge volume (unless precluded by stormwater management limitations listed
in this Section)
Stormwater discharge of Total Suspended Solids (TSS)
Stormwater discharge of Total Phosphorus (TP)
Methods for Volume Control:
CN Reduction Credits:
All sites shall consider the use of curve number (CN) reduction credits as a portion of the volume
control requirement. These methods include tree plantings, native grass buffers, porous pavements,
impervious disconnections, green roofs, constructed wetlands, and soil amendments.
Credit for each method is given on an area basis at the following depths: An example of the credit
reduction can be found in Section 9.
tree plantings 0.05 inch
native grass buffers 0.05 inch
natural area preservation 0.05 inch
soil amendments 0.05 inch
impervious disconnection 0.10 inch
porous pavements 0.50 inch + not counted in impervious calculation
green roofs 1.00 inch + not counted in impervious calculation
An example of the credit reduction can be found in Section Nine, Miscellaneous and CN Reductions.
Each CN reduction method has additional requirements described in Section 9. Additional CN
reduction techniques may be proposed., cApproval of such techniques and assignment of cCredits
will be at the discretion of the EngineerCity.
Greywater/Stormwater Recycling:
For many applications, the use of pond water for irrigation can be a very cost effective method of
volume control (reduces monthly water bills and construction cost for infiltration areas). Since these
systems do not directly function on a storm by storm basis an applicant is asked tomust work with the
Engineer City to determine the required amount of volume standardcontrol credit to be applied.
Infiltration:
If infiltration is used the following is required:
1. Requirements and recommendations laid out in the Minnesota Stormwater Manual shall be
followed.
2. Infiltration tests shall be used to provide a base infiltration rate of surrounding soils. The base
rate shall be reduced to a conservative rate for the design. The Iinfiltration tests shall be
conducted at the location and elevation of the proposed infiltration system.
Bioretention:
If Bbioretention is used the following is required:
1. Requirements and recommendations laid out in the Minnesota Stormwater Manual shall be
followed.
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Public Works Design Manual
Adopted July 16, 2007
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2. Infiltration tests shall be used to provide a base infiltration rate of surrounding soils. The base
rate shall be reduced to a conservative rate for the design.
Stormwater Wetlands/ Constructed Wetlands:
Constructed wetlands may be utilized to abstract volume. Since these systems do not directly
function on a storm by storm basis an applicant is asked tomust work with the Engineer City to
determine the required amount of volume standardcontrol credit to be applied.
1. Requirements and recommendations laid out in the Minnesota Stormwater Manual shall be
followed.
Offsite Volume ControlStormwater Management:
For Qualifying Small Sites, aAny of the above credits can be used at an offsite location to meet the
volume control requirement with the approval of the City Engineer. The offsite location must be within
the same watershed. Off siteOffsite volume controlBMPs should must be permanently protected
through an easement, development agreement and/or maintenance agreement, to help ensure the
volume reduction feature continues to function as designed.
For NPDES Permit Sites, offsite stormwater management may be allowed for meeting TSS and/or
TP reduction requirements [MS4 Permit, Part III.D.5.a(4)].
Stormwater Management Overlay District #2 – All Landlocked Basins
If a development is in a tributary area to a landlocked basin, the following restricted volume control is
required for that tributary area portion:
Volume shall be reduced in the proposed condition by a volume equal to or greater than 1.0
inches per _________ over all new impervious surfaces.
Extended duration detention is required such that volume discharging offsite in the proposed
condition not exceed the volume discharging offsite in the existing conditions in the 24 hour
period following the peak of the 100-year, 24 hour rainfall event (NRCS Type II stormMSE3
rainfall distribution).
Provision of an outlet or emergency overflow does not reduce the amount of Additional Volume
Control required. under this rule is not waived if an outlet or emergency overflow is provided..
Stormwater Management Limitations on Volume Control Methodand Exceptions:
The method or location of Volume Control used may be limited by the following:
Infiltration techniques to achieve volume control requirements are prohibited when infiltration BMPs
will receive discharges from, or are constructed in areas:
Where industrial facilities are not authorized to infiltrate industrial stormwater under an
NPDES/SDS Industrial Stormwater Permit issued by the MPCA
Where vehicle fueling and maintenance occur
With less than 3 feet of separation distance from the bottom of the infiltration system to the
elevation of seasonally saturated soils or the top of bedrock
Where high levels of contaminants in soil or groundwater will be mobilized by the infiltrating
stormwater
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Infiltration techniques to achieve volume control requirements, (without higher engineering review
and City approval), sufficient to provide a functioning treatment system and prevent adverse impacts
to groundwater, are restricted when the infiltration BMPs will be constructed in areas:
With predominately Hydrologic Soil Group D (clay) soils
Within 1,000 feet up-gradient, or 100 feet down-gradient of active karst features
Within a Drinking Water Supply Management Area (DWSMA) as defined in Minn. R.
4720.5100, subp. 13
Where soil infiltration rates are more than 8.3 inches per hour
For linear projects where the lack of right-of-way precludes the installation of volume control practices
that meet the volume control requirements, and a reasonable attempt has been made to obtain right-
of-way during the project planning process, exceptions for stormwater discharge volume under the
following circumstances:
The owner and/or operator of a construction activity is precluded from infiltrating stormwater
through a designed system due to any of the infiltration-related limitations described above,
and;
The owner and/or operator of the construction activity implements, to the maximum extent
practicable, volume reduction techniques other than infiltration on the site of the original
construction activity that reduces stormwater discharge volume, but may not meet the volume
control requirements.
Groundwater table within 3’ of soil infiltration feature:
Infiltration features should be sited with the aid of soil boring information and infiltration tests
on soils representative of those in the vicinity of the proposed basin.
Wellhead protection area:
Soil infiltration features must comply with requirements and limitations of wellhead protections
plans.
Impervious Soils:
Surface infiltration features must have appropriate soils. In the case of type D/clay soils
Surface infiltration is not allowed.
Stormwater Mitigation Provisions
Stormwater mitigation provisions shall apply to all NPDES Permit Sites, as defined in this section.
Stormwater mitigation shall comply with the MS4 Permit, Part III.D.5.a(4), Mitigation Provisions (page
17 of 38).
Long-Term Maintenance of Structural Stormwater BMPs
Structural stormwater BMPs not owned or operated by the City of Prior Lake that were implemented
to meet the conditions for post-construction stormwater management in the MS4 Permit, Part
III.D.5.a(2) shall comply with the MS4 Permit, Part III.D.5.a(5).
4.4 Low Floor / Low Opening Elevations
Low Floor Elevations and Low Opening Elevations are to be designed to the following standards:
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Low floor elevations shall be at least:
3’ Above OHW or Highest Known (whichever is greater)
2’ Above HWL
Low opening elevations shall be at least:
2’ Above E.O.FEOF
In the case of a landlocked basin, low floor elevations shall be at least:
3’ above the basin overflow elevation or 3’ above the back to back 100- year, 24-hour rainfall
events (NRCS MSE3 rainfall distribution flood.
4.5 Additional Requirements
In the development of any subdivision or ponding areaFor development or redevelopment projects,
the developer and/or property owner is responsible for the removal of all significant vegetation (trees,
stumps, brush, debris, etc.) from any and all areas which would be inundated by the designated
controlled outlet elevation (OE) of any required ponding areas as well as the removal of all dead trees,
vegetation, etc., to the high water level (HWL) of the pond.
Upon the completion of the construction of a designated ponding areaStructural Stormwater BMP,
the developer is required to submit an as-built record plan of the ponding area certifying that the pond
Structural Stormwater BMP constructed meets all design parameters. The Ddeveloper can may over-
excavate the bottom of the water qualitystormwater ponds to compensate for erosion that will occur.
The Ddeveloper will be responsible for verifying, at the end of the W warranty Pperiod, that the ponds
are providing the required volume.
4.6 Water Quality
The water quality treatment standard for new stormwater ponds is a 60% reduction in Total
Phosphorus (TP) and 90% reduction in Total Suspended Solids (TSS) from the proposed developed
area draining to a stormwater pond. Section 7 Seven, Stormwater Pond Design Criteria, details
standard wet pool detention pond design criteria.
Alternatives to water qualitystormwater ponds can may be proposed but must meet water quality
treatment standards. If alternatives are proposed, documentation must be submitted by the applicant
based on literature values or independent laboratory work to demonstrate the performance of the
alternative being proposed.
SECTION FIVE:
DRAINAGE ALTERATIONS AND FLOODPLAIN MANAGMENT
5.1 Landlocked Basins
If a landlocked basin (tributary area < 25 acres) is proposed to be connected to a downstream system
the following is required:
If the landlocked basin contains a wetland, the rate of outflow from that wetland must follow
provisions for the “Alternate Rate Control Standard for Wetlands utilized for Volume
Management” detailed in Section 4.
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If the landlocked basin contains a wetland, Stormwater Utilization must occur to the maximum
extent allowable under provisions for wetlands detailed in Section 6.
If the landlocked basin does not contain a wetland, or the wetland is legally proposed to be
filled under the Wetland Conservation act, the volume storage lost to connection must be
mitigated by increasing volume storage of a pond or wetland equal to the lost volume of the
landlocked basin utilized in the 100 year storm event.
All Provisions described in Section 5, Drainage Alterations must be followed.
If a landlocked basin (tributary area > 25 acres) is proposed to be connected to a downstream system
the following is required.
All requirements listed above apply.
The PLSLWD or Scott WMO must review the proposed connection. All conditions of Scott
WMO or PLSLWD approval must be met.
5.2 Drainage Alterations
If the applicant proposes to artificially drain, connect a landlocked basin, obstruct, or redirect the
natural flow of runoff the following is required:
Drainage alteration (tributary area < 5 acres) requirements:
Demonstrate:
That overall change in flow volumes to each subwatershed do not burden downstream
infrastructure.
Requirements:
Considered a minor alteration provided applicant demonstrates that downstream burdens do
not exist.
If there is evidence to suggest there is or will be a flooding problem immediately downstream
of the proposed alteration, the requirements for drainage alteration of between 5 and 25 acres
shall apply.
Drainage alteration (tributary area > 5 and < 25 acres):
All requirements listed above apply.
Demonstrate:
There is a necessity for such a change.
Reasonable care has been taken to avoid impact to upstream or downstream land.
Efforts have been taken to mitigate changes in downstream volume and rates.
Requirements:
City approval of drainage alterations is required.
Peak rate to the gaining subwatershed of the drainage alteration must be held to rate control
standard per tributary acre included in the development.
Drainage alteration (tributary area > 25 acres) requirements:
All requirements listed above apply.
The PLSLWD or Scott WMO must approve the proposed alteration. All conditions of Scott
WMO or PLSLWD approval must be met.
5.3 Floodplain Alterations
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If grading takes place within the floodplain (below the predicted 100-year flood elevation for a public
water) no net decrease in flood storage is allowed.
SECTION SIX:
WETLANDS
6.1 Procedure
For developments near wetlands, tThe following procedure is dependent on which Watershed the
location of the wetland(s) falls. Some requirements, common to both Scott WMO and PLSLWD are
listed under “both.” To determine which watershed a requirements apply to a project is in, refer to
Figure 2applicants should contact the City early in the planning process.
Stormwater susceptibility is determined from the results of a wetland functional assessment
(Minnesota Routine Assessment, or MnRAM) to determine if a wetland is eligible for stormwater
utilization.
Both:
The applicant must submit a wetland delineation and a MnRAM 3.0 wetland functional assessment;
these documents are then reviewed by the City.
If impacts are proposed to any wetland, the procedure follows the requirements of the Wetland
Conservation Act and these rules.
A wetland is given a functional classification dependent on the value for vegetative diversity
determined by the MnRAM 3.0. Rankings are: Exceptional, High, Medium, and Low.
6.2 Requirements
PLSLWD:
Wetland replacement for impacts occurring within the PLSLWD must take place within the District at
a rate of 0.5:1 (New Wetland Credit per acre impacted.)
Both:
The City must review and approve of the wetland delineation and Minnesota Routine Assessment
Version 3.0, (MnRAM) (as amended) results.
Any drainage, fill, excavation or other alteration of a public waters or wetlands is regulated by the
Wetland Conservation Act (WCA), State Statutes 103G.245 and regulations adopted hereunder. The
City is the Local Governing Unit (LGU) under these rules.
A conservation easement is required over all buffers. Conservation easements shall be dedicated to
the PLSLWD in District areas or to the City in WMO areas.
6.3 Stormwater Susceptibility.
Both:
Highly Susceptible: A wetland is considered highly susceptible if:
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Forty percent or more of the wetland complex has highly susceptible wetland communities as
shown in Table 6.1 and;
Highly susceptible wetland communities have medium to exceptional floral diversity/integrity.
Moderately Susceptible: A wetland is considered moderately susceptible if:
Forty percent or more of the wetland complex has a moderately susceptible wetland
communities shown in Table 6.1 and;
Moderately susceptible wetland communities have medium to exceptional floral
diversity/integrity.
Least Susceptible: Wetlands with low floral diversity, as determined by MnRAM, were considered to
be least susceptible wetlands.
Slightly Susceptible: Wetlands that do no fall under the high, moderate or least susceptible categories
are considered slightly susceptible.
Table 6.1
Wetland Community Susceptibility to Stormwater Impacts
Highly Susceptible Wetland Communities* Moderately Susceptible Wetland
Communities*
Sedge Meadow Low Prairies Shrub-Carrs
Bogs Coniferous Swamps Alder Thickets
Coniferous Bogs Hardwood Swamps Fresh (wet) Meadows
Open Bogs Seasonally Flooded Basins Shallow Marsh
Calcareous Fens Deep Marsh
Wetland communities determined using key provided in MnRAM Version 3.0.
6.4 Stormwater Utilization:
Table 6.2
Stormwater Utilization
Hydroperiod
Standard
Highly
Susceptible
Moderately
Susceptible
Slightly
Susceptible
Least
Susceptible
100-year Storm
Bounce
Existing Existing + 0.5 ft Existing + 1.0 ft No Limit
Discharge Rate Existing Section 4:
Wetland
Standard (1)
Section 4:
Wetland
Standard (1)
Section 4:
Wetland
Standard (1)
1 & 2 year NRCS
event Inundation
Existing Existing + 1 Day Existing + 2 Days Existing + 7 Days
10 yr NRCS
event Inundation
Existing Existing + 7 Days Existing + 14
Days
Existing + 21
Days
(2) Outlet Control
Elevation
None: Note
OE/HWL on Map
None: Note
OE/HWL on Map
0 – 2 ft additional
storage
0 – 4 ft additional
storage
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(1) Rates shall be held to the rate control spelled out inrequirements of Ssection 4, alternate rate
control standard for wetlands, unless obtaining these rates is prevented by inundation period
requirement.
(2) Outlet Control Elevation changes can be made to mitigate volume storage as required in
Section 5.
6.5 Buffer & No-Grade Zone Requirements
PLSLWD:
The following are the buffer and minimum no-grade zone requirements for each functional
classification. The tiered buffer requirement is based on a functional classification of; exceptional,
high, medium or low, and can be found using the results of the MnRAM vegetation assessment as
described above
Table 6.3
PLSLWD Buffer, Setback and No-Grade Matrix
Buffer
Requirement
Exceptional High Medium Low
Average Buffer
Width (ft)
30 30 30 30
Minimum Buffer
Width (ft)
20 20 20 20
Minimum No-
Grade Zone (ft)
10 10 10 10
Foundation
setback from
Buffer
20 20 20 20
Scott WMO:
The following are the buffer and minimum no-grade zone requirements for each functional
classification. The tiered buffer requirement is based on a functional classification of; exceptional,
high, medium or low, and can be found using the results of the MnRAM vegetation assessment as
described above.
Table 6.4
Scott WMO Buffer, Setback and No-Grade Matrix
Buffer
Requirement
Exceptional High Medium Low
Average Buffer
Width (ft)
65 50 30 25
Minimum Buffer
Width (ft)
25 25 25 25
Minimum No-
Grade Zone (ft)
25 25 25 25
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Foundation
setback from
wetland
35 35 35 35
Both:
Grade changes or other disturbances are not allowed in Nno-Ggrade Zzones with the following
exceptions: Pipe Ooutlets and associated riprap, reseeding or soil amendments, embankment and
impacts associated with an approved CIP transportation corridor, grade changes adjacent to
approved WCA impacts to wetlands, approved wetland or flood storage mitigation areas and
temporary impacts associated with utility installation.
A buffer width may vary using “Buffer Averaging.” Buffer width may be reduced to the minimum buffer
width, but the overall buffer area must be equal in area to a hypothetical fixed width average buffer
around the same wetland. This means that while one side of a buffer is reduced in width, the buffer
must be increased in width in another area to make up for the loss of area.
6.6 Buffer Vegetation Requirements:
Both:
Buffer must be seeded with a native mix with forbs. A two year maintenance period is required as
part of the developers agreement or other City agreement. If at the end of the two year maintenance
period the seed has not established, there is a prevalence of invasive species, or there are other
encroachments, over-seeding or reseeding may be required.
Land use within a buffer shall be subject to the following restrictions: Buffer vegetation shall not be
cropped, cultivated, hayed, mowed, fertilized, or subject to the placement of mulch or yard waste or
otherwise disturbed, except for the periodic cutting or burning that promotes the vegetative health of
the buffer or as needed to address invasive or noxious species. Buffers may be temporarily disturbed
when permitted by the City Engineer. No new structure or hard cover may be placed within a buffer
area. No fill, debris, or other material may be excavated from or placed in a buffer area.
Buffer strips shall be required whether or not the wetland is on the same parcel as the proposed
development or on an adjacent parcel. Wetlands on adjacent parcels need not be delineated, but an
estimation using aerial photos or other methods will be required.
If acceptable vegetation is in place, reseeding is not required. Acceptable natural vegetation has the
following characteristics: A continuous dense layer of perennial grass uncultivated or unbroken for 5
years or has an overstory of trees of shrubs uncultivated or unbroken for 5 years.
6.7 Buffer Monuments and Easement:
Both:
Buffer strips shall be identified within each parcel by permanent monumentsation. A monument shall
be required at each parcel line where it crosses a buffer strip and shall have a maximum spacing of
200 feet along the edge of the buffer strip. An additional monument shall be placed at the midpoint
of each lot and/or as necessary to accurately define the edge of the buffer strip. (considering
curvature). A monument shall consist of a post and a buffer strip sign. The signs shall be 4.5” x 6.5”
inch vertical, have brown field with white lettering, and shall be securely mounted on a post to a
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minimum height of 4 feet above gradecomply with City Plate #203, Wetland Boundary Signs. The
signs shall include warnings about disturbing or developing the buffer strip. The signs shall be
installed prior to the issuance of a Building Permit and should be shown on the approved plans. Buffer
strip signs can must be purchased at the Engineering Divisionfrom the City at a cost shown on the
latest fee schedule.
All buffer strips must be covered by drainage and utility easement and conservation easements.
Drainage and utility easement shall be granted to the City of Prior Lake. Conservation easements
shall be dedicated to the PLSLWD in District areas or to the City in WMO areas.
SECTION SEVEN:
STORMWATER POND DESIGN CRITERIA
Water Quality Volume
The permanent pool volume for water qualitystormwater ponds shall be calculated using the Design
Calculations for Wet Detention Ponds by Dr. William W. Walker (1987) presented below.
WA Total Watershed area (acres)
iA Area of impervious surfaces draining to stormwater conveyors (acres)
iF Impervious Fraction
w
i
A
A
CN area weighted mean NRCS curve number for pervious portion of watershed (Based on soil
type and land cover)
P= Design storm size =2.5 (inches)
101000
CNS Maximum soil retention (inches)
iiFSP
SPFPR
18.0
2.0 2
= Runoff for design storm (inches)
12
wARV Volume of permanent pool (acre-feet)
Rate Control Volume
The active volume (between the OE and the HWL) shall be sized to meet the rate control requirements
outlined in Section 4, Rate Control, using a maximum slope at 4:1 (H:V).
Additional Design Criteria
The use of regional ponding, stormwater wetlands, or expandable ponding is encouraged by the City.
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A 10’ wide aquatic vegetation bench is required below the OE of the pond, with the maximum slope
of 10:1.
The invert elevations of pond inlet flared end sections shall match the OE of the pond. Submerged
outlets will only be allowed at the discretion of the City Engineer.
Outlet control structures from ponding areas are required as directed by the City. Location and
appearance of outlet structures shall be subject to City approval and may require landsc ape
screening.
The E.O.FEOF of a pond should be at least 1 foot higher than the HWL. The top of dike elevation
should be at least 2 feet higher than the HWL.
Dikes used to create rate control ponds must at maximum use 4:1 slopes and measure 10’ wide at
top. At minimum, a clay core should be designed in consideration of groundwater flow. If head
difference between OE of pond and downstream land exceeds 3’, soils data will be required in the
area and dike design must address maintenance of pond water level and dike stability. Outlet pipes
through engineered dikes with head differences greater than 6’ should be designed with anti-seep
collars. Sand bedding shall not be used through dike section.
Pond outlets shall provide floatable debris skimming for the 10- year, 24-hour rainfall event (NRCS
MSE3 rainfall distribution). A manhole with a baffle wall with orifice or notch is recommended to
control rate. Outlet rate control manholes shall have a top mitered to conform to fill. A 66” minimum
diameter is required to provide access to both sides of the weir wall.
SECTION EIGHT:
STORM SEWER DESIGN CRITERIA
Storm water sewer facilities shall use design criteria utilizing a rational or hydrograph method based
on sound hydrologic theory to analyze the storm water runoff and proposed development. (Such as
the Soil Conservation Service TR-55 Urban Hydrology for Small Watersheds)
Storm water sewer facilities shall be designed for a 10-year, 24-hour frequency stormrainfall event
(NRCS MSE3 rainfall distribution) for local pipe design and a 100-year, 24-hour rainfall event (NRCS
MSE3 rainfall distribution) frequency storm for ponding detention basin design and trunk facilities.
Pipe size and grade shall be greater than 15” ID and 0.5% slope. Pipe class shall conform to design
standards as shown in “EXHIBIT M”.
Drainage calculations shall be submitted to show the sizing of pipe, ponds, emergency overflow
spillways, and catch basin interception analysis. Assuming catch basins can receive a maximum of
3 cfs, multiple catch basins may be required at low points.
Provide for overflow routes to drain all street and backyard low points.
SECTION NINE:
MISCELLANEOUS AND CN REDUCTIONS
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Chapter Section 4 detailed a credit system used for volume management; the following is additional
information on that credit system.
Example calculation for CN Reduction: The following calculation is an example of volume control met
entirely through the use of CN reductions., Tthis will not be suitable for most sites but serves as an
example on how to use a variety of methods to meet the requirement.
50 acre site with 20% impervious surfaces, = 10 acres new impervious (actual calculation required)
10 acres impervious x 0.5in volume control requirement = 5ac-in or 18150cf volume.
(see next page for sample calculation)
Volume CreditsReductions Claimed:
CN Reduction ClaimedCategory Area (acres) Area basis depth (in) Credit (ac-in)
5 acres Nnative grass buffers 5 0.05 0.25
1 acre of proposed Ppervious
pavers
1 0.50 0.50
Same Pervious paver area no
longer counted in impervious
calculation
1 0.50 0.50
5 acres Ttree plantings (436 trees) 5 0.05 0.25
30 acres of Ssoil amendments 30 0.05 1.50
5 acres of Iimpervious area
disconnections
5 0.10 0.50
1 acre Ggreen roof 1 1.00 1.00
Same Ggreen roof area no longer
counted in impervious calculation
1 0.50 0.50
Total ClaimedVolume Credits: 5.00 ac-in
Additional Requirements for CN Reduction
Tree plantings:
Area determinations for tree plantings shall be assumed at 500sf per tree. (Based on an conservative
average water use of 1cf per day per tree at 7 years in an open canopy condition, less average tree
mortality, 3days water use per storm 0.7*(1/(.05/12))*3 the beneficial effects of canopy intercept are
ignored). This reduction can be used in combination with the native grass buffer (ex. Oak prairie
restoration could count as tree planting, native grass and soil amendment reduction).
Native grass buffers:
Area determination shall only include buffers currently, or proposed to be, established in a native
species. Area must be included in a permanent conservation easement dedicated to the City of or
Watershed DistrictPLSLWD.
Natural area preservation:
Upland wooded or prairie areas proposed include only those areas not already prohibited from
development (buffers, bluffs, etc.) and must be kept in their natural state through outlet outlot
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dedication and/or conservation easements. No grading is allowed in preservation areas.
Preservation area must be denoted through the use of decorative fencing, informational signing, or
other methods approved by the City.
Soil amendments:
Area determinations for soil amendments shall include only those areas from the back of building
pads to the grading limits in the rear. For areas in front and side, or under temporary constriction
access to be counted, sSoil amendments must take place after building constructions is compete,
due to the compactive nature of hometo avoid compaction during the construction process.
Soil amendment shall be designed to mitigate the effects of compaction due to mass grading by
returning the soil to a loose, friable state able to transmit water.
All soil amendments must be designed by a registered licensed professional engineer or professional
soil scientist. Soil design must promote deep loosening of the mass-graded soils strata, and
improvement of infiltration and moisture retention characteristics of the topsoil. (Example: 18” deep
ripping or tilling of base soils and compost mix after mass grading, followed by the application of a
designed mix of compost, peat, sand, and topsoil and spread at 6” depth).
Impervious disconnection:
Area determination for impervious disconnections will be that roof area or select pavement area that
is disconnected from the drainage system and allowed to flow over natural grounds that are designed
to promote infiltration and transpiration. Design shall not cause nuisance, wet lawn conditions, or
basement seepage, or other nuisances. Design must discourage reconnection to impervious
surfaces by providing a minimum of a 75’ pervious flow path.
Porous pavements:
Area determination for porous pavements will be only that area meeting the following requirements:
Porous pavement systems must use permeable base material and promote infiltration. Porous
pavements must be designed by a licensed professional engineer and approved by the City Engineer.
Green roofs:
Area determination for green roofs will be only that area meeting the following requirements: Design
must be must be designed by a professional architect and meet Building Code. The design must be
approved by the City Engineer.
(More information on these and other CN reductions and site design measures can be found in
Chapters 4 and 11 or the MPCA stormwater manual).
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PART III
HYDROLOGY RULES
Site hydrology must follow the rules specified herein. These rules are based on the policies set forth
in the City of Prior Lake Local Surface Water Management Plan (LSWMP), the Water Resource
Management Plan of the Prior Lake-Spring Lake Watershed District (PLSLWD), and the
Comprehensive Water Resource Management Plan and Rules of the Scott Water Management
Organization (Scott WMO).
By enforcing the rules of this Part, the City of Prior Lake is fulfilling the requirements of State Statute
Chapters 103Band 103D and Minnesota Rules Chapter 8410. The City of Prior Lake enforces these
rules under the terms of a Memorandum of Understanding or Memorandum of Agreement (MOU or
MOA) with both the PLSLWD and Scott WMO.
In the future, when major amendments are needed in this Part, the Scott WMO and the PLSLWD
must be consulted and must grant approval for said amendments as required by Scott WMO,
PLSLWD, State Statute, and Minnesota Rules.
Index of Sections
Section One Definitions
Section Two Format and Standards
Section Three Grading, Erosions and Sediment Control
Section Four Site Hydrology and Stormwater and Volume Management
Section Five Drainage Alterations and Floodplain Management
Section Six Wetlands
Section Seven Pond Design Criteria
Section Eight Storm Sewer Design Criteria
Section Nine Miscellaneous and CN Reductions
SECTION ONE:
DEFINITIONS
Best Management Practices (BMPs): Practices to prevent or reduce the pollution of the waters of the
state, including schedules of activities, prohibition of practices, management practices, treatment,
requirements, and operating procedures and practices to control plant site runoff, spillage or leaks,
sludge, or waste disposal or drainage from raw material storage. BMPs include practices documented
in the Minnesota Stormwater Manual (MPCA), Protecting Water Quality in Urban Areas (MPCA,
2000), and other MPCA manuals, all as amended.
Buffer: An area of natural, non-invasive, permanently undisturbed, vegetated ground cover adjoining
and surrounding a wetland measured from the delineated edge of the wetland.
Buffer Averaging: Varying the width of a buffer while maintaining compliance with all buffer
requirements outlined in Section Six, Wetlands. A buffer around a wetland may have variable width
as long as any minimum buffer width requirements are met. The overall buffer area must be equal in
area to a corresponding fixed width buffer around the same wetland, set at the average width.
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Common Plan of Development or Sale: A contiguous area where multiple separate and distinct land
disturbing activities may be taking place at different times, on different schedules, but under one
proposed plan. One plan is broadly defined to included design, permit application, advertisement or
physical demarcation indicating that land disturbing activities may occur.
Construction Activity: A disturbance to the land that results in a change in the topography, existing
soil cover (both vegetative and non-vegetative), or the existing soil topography that may result in
accelerated stormwater runoff, leading to soil erosion and movement of sediment into surface waters
or drainage systems. Examples of construction activity may include clearing, grading, filling, and
excavating.
EOF: Emergency Overflow.
Expandable Ponding: Ponds built in low areas common to multiple developments that can be easily
expanded when neighboring areas develop.
HWL: High water level of a pond or basin resulting from the 100-year, 24-hour storm.
Landlocked Basin: Any depression with a contributing drainage area greater than 1 acre that does
not have a natural surface outflow below the level of the 100-year, 24-hour storm, or below its OHW.
LSWMP: Local Surface Water Management Plan.
Maintained Area: Turf grass or landscaped area that receives regular maintenance such as mowing
or mulching.
MS4 Permit: MPCA General Permit authorizing the discharge of stormwater associated with small
Municipal Separate Storm Sewer Systems (MS4) under the NPDES/SDS permit program; Permit No.
MNR040000.
Net Acre: Total land area minus any wetland, lake, or bluff acreage.
New Development: All construction activity that is not defined as redevelopment.
No-grade zone: An area around a wetland where no change in grade is allowed.
NPDES Construction Stormwater Permit: MPCA General Permit authorizing the discharge of
stormwater associated with construction activity under the NPDES/SDS Program; Permit No.
MNR100001.
NWL: Normal water level, the elevation of the permanent wet pool of for a pond or basin.
OE: Outlet Elevation, the primary outlet elevation of a pond or basin.
OHW : Ordinary High Water level.
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Qualifying Small Sites: Sites where development, redevelopment, or change in use creates more
than 3,500 square feet of new impervious area and disturbs more than 10,000 square feet of land,
but where coverage under the NPDES Construction Stormwater Permit is not required.
Redevelopment: Any construction activity where, prior to the start of construction, the areas to be
disturbed have 15 percent or more of impervious surface(s).
Reduce: Reduce to the Maximum Extent Practicable (MEP) unless otherwise defined in the context
in which it is used.
Regional ponding: Permanent stormwater facility used to provide rate control and water quality
treatment for an area that encompasses two or more entities (including but not limited to
developments, subdivisions, building additions, and conditional uses).
Stormwater: Stormwater runoff, snow melt runoff, and surface runoff and drainage.
Stormwater Management Overlay District: An area within the City that has a separate set of
standards, generally defined by a tributary feature (Example: Any area draining to the Prior Lake
Outlet Channel).
Structural Stormwater BMP: A stationary and permanent BMP that is designed, constructed, and
operated to prevent or reduce the discharge of pollutants in stormwater.
Swale: A wide, shallow, vegetated depression in the ground designed to channel drainage of water.
Tributary Area: Total land area that drains into a pond, wetland, ditch, stream, reach, or other point
of interest on site in the existing condition, prior to any drainage alterations or landlocked basin
connections.
Volume Management: Limiting volume and rate of stormwater by impounding water for extended
durations within a tributary area.
Volume Storage: Volume set aside for holding stormwater below a natural or created outfall that
during hydrologic variation mitigates effects of increased stormwater volume.
SECTION TWO:
FORMAT AND STANDARDS
2.1 Construction Drawings
Show the OE and HWL for ponds and the OHW for water bodies on the plans.
Show garage floor, low floor, and rear pad elevations and housing style for each unit on the grading
plan. Include a schematic describing each housing style and typical grading.
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Show limits of clearing and limits of grading on grading plan and tree preservation plan. Show removal
of all trees and brush that will occur below the NWL of existing and newly created ponding areas.
Show emergency overflow routes using arrows from all low points and show elevation of high point
along emergency overflow route. All emergency overflow routes shall be graded and the easement
area sodded prior to Building Permit issuance.
Show or define access routes for maintenance purposes to all stormwater infrastructure and ponding
areas (maximum of 8% grade, maximum of 2% cross slope, and minimum of 10’ wide). Drainage and
utility easements shall be dedicated at the time of final platting to provide this access.
2.2 Stormwater Management Report
Calculations shall be submitted showing proposed design elements that meet requirements of this
Part. A narrative describing the proposed system shall accompany this collection of calculations.
The stormwater narrative shall be a brief and clear description of the stormwater system that
summarizes and reference figures, tables and plan sheets. The following are the minimum
summary/narrative elements:
Narrative describing the proposed system, referencing requirements in this Part
Summary of existing and proposed offsite runoff rates and volumes
Summary of volume control requirements and curve number reductions claimed
Narrative describing volume control method and why it was chosen
Summary of volume control system showing that it meets requirements
Existing and proposed drainage maps
Walker method calculations
SECTION THREE:
GRADING, EROSION AND SEDIMENT CONTROL
Site erosion and sediment control described here is in addition to the Stormwater Pollution Prevention
Plan (SWPPP) as required by the NPDES Construction Stormwater Permit. All sites must comply
with the NPDES Construction Stormwater Permit regardless of whether the builder/developer is party
to the Permit.
3.1 Grading Standards
Maximum 4:1 slopes are allowed in “maintained” areas except approved by the City. Maximum 3:1
slopes are allowed for road fill sections adjacent to water bodies, buffers, or other areas permanently
protected by easements or City ownership.
Minimum grade for swales and lot grading shall be 2% or greater. Drainage swales shall have a
maximum length of the greater of: (i) 300 feet; (ii) a total of eight lots draining to a point; or (iii)as
approved by the City. Backyard drainage structures should be avoided. Drainage swales shall be
graded and stabilized (drainage blanket, seed and mulch, or sod) prior to the issuance of Building
Permits.
A minimum of 15 feet beyond the house pad shall have a slope less than 10:1.
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Verify locations and design of all overland drainage routes for capacity and erosion potential. All low
points in streets must have E.O.F’s designed for the 100 year storm event.
3.2 Erosion and Sediment Control / SWPPP Standards.
All construction activity that results in land disturbance of equal to or greater than 1 acre or a common
plan of development or sale that disturbs greater than 1 acre must comply with the requirements of
the NPDES Construction Stormwater Permit. The SWPPP must be reviewed and approved by the
City before an Excavating and Grading Permit is issued.
An SWPPP that meets the requirements of the NPDES Construction Stormwater Permit must be
prepared for all construction activity that results in land disturbance of equal to or greater than 10,000
square feet in a shoreland zone. The SWPPP must be reviewed and approved by the City before an
Excavating and Grading Permit is issued.
All provisions of the NPDES Construction Stormwater Permit & SWPPP must be adhered to for the
duration of the City grading permit.
Provide name of company, contact person, and phone number for person responsible for SWPPP
preparation, implementation, and maintenance.
Provide a note on the plans specifying that all down gradient sediment control BMPs shall be installed
prior to any land disturbance. The City must inspect and approve these BMPs before land disturbance
may occur.
Slopes greater than or equal to 4:1 shall have erosion control blanket installed immediately after
finished grading.
Areas coming out of agricultural production must be seeded with a cover crop prior to development.
SECTION FOUR:
SITE HYDROLOGY, STORMWATER AND VOLUME MANAGEMENT
4.1 General Standards
A hydrologic method, based on sound hydrologic theory must be used to analyze runoff for the design
of stormwater conveyance systems and permanent stormwater facilities. Curve numbers shall follow
recommendations of SCS Technical Release 55, Second Edition (TR-55, 1986).
Rate and volume control will be required for all development, redevelopment, or change in use that
creates more than 3,500 square feet of new impervious area and disturbs more than 10,000 square
feet of land. Sites exceeding these thresholds that do not require coverage under the NPDES
Construction Stormwater Permit are termed Qualifying Small Sites.
4.2 Rate Control
NOAA Atlas 14 precipitation depths resulting from the 2-, 10- and 100-year, 24-hour storm events
(NRCS MSE3 rainfall distribution) shall be modeled for existing and proposed conditions. NOAA
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Atlas 14 precipitation depths for Prior Lake are 2.84”, 4.22” and 7.39” for the 2-, 10- and 100-year,
24-hour storm events, respectively.
Rate Control Standard:
Discharge rates for the 2-, 10-, and 100-year, 24-hour storm events existing before the proposed
development, redevelopment, or change in use shall not be increased.
Stormwater Management Overlay District #1 – Prior Lake Outlet Channel: (Figure 1)
Rate control for tributary areas to the Prior Lake Outlet Channel shall hold total offsite peak runoff at
or below the following schedule:
2-year, 24-hour event: 0.25 cfs per net acre
10-year, 24-hour event: 0.25 cfs per net acre
100-year, 24-hour event: 0.25 cfs per net acre
Alternate Rate Control Standard for Wetlands Utilized for Volume Management:
A portion of the 10- and 100-year, 24-hour storm events from a development may utilize wetlands for
stormwater rate control. The wetland must be eligible based on the requirements of Section Six,
Wetlands. The following schedule shall apply to the rate control a wetland provides.
The Alternate Standard for Wetlands shall hold discharge out of a utilized wetland at or below the
following rate schedule:
2 year: 0.05 cfs per tributary acre
10 year: 0.15 cfs per tributary acre *
100 year: Existing peak flow *
* May be overridden by a stormwater management overlay district.
* In the case that the wetland cannot provide the volume for active storage in the 10- and 100-year
storms, the upstream stormwater system must be sized such that the system meets this requirement.
Any proposed improvements utilizing wetlands for portions of the 10- or 100-year event storage must
consider the build out condition of the watershed draining to that wetland. Developments will be
allowed to utilize a wetland proportional to their share of the tributary area. Rate control must be
constructed to serve the build-out condition of the entire subwatershed based on current zoning.
Information on the utilization of wetlands for volume storage can be found in Section 6 of this Part.
Wetlands may not be eligible for utilization if land ownership or easements for stormwater uses cannot
be obtained.
Additional requirements for rate control may be set by the City. The utilization of wetlands for active
storage or volume storage is subject to the approval of the City.
4.3 Volume Control
Volume Control Standard 1 – Qualifying Small Sites:
Applies to qualifying small sites as defined in this Section. Site runoff volume for qualifying small sites
shall be reduced from pre-project conditions by a volume equal to or greater than 0.5 inch over all
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new impervious surfaces, unless that standard is modified by a Stormwater Management Overlay
District.
Volume Control Standard 2 – NPDES Permit Sites:
Applies to new development and redevelopment projects with land disturbance of greater than or
equal to 1 acre, including projects less than 1 acre that are part of a larger common plan of
development or sale and that discharge to the Prior Lake MS4.
For new development projects, site runoff shall have no net increase from pre-project conditions (on
an annual average basis) of:
Stormwater discharge volume (unless precluded by stormwater management limitations listed
in this Section)
Stormwater discharge of Total Suspended Solids (TSS)
Stormwater discharge of Total Phosphorus (TP)
For redevelopment projects, site runoff shall have a net reduction from pre-project conditions (on an
annual average basis) of:
Stormwater discharge volume (unless precluded by stormwater management limitations listed
in this Section)
Stormwater discharge of Total Suspended Solids (TSS)
Stormwater discharge of Total Phosphorus (TP)
Methods for Volume Control:
CN Reduction Credits:
All sites shall consider the use of curve number (CN) reduction credits as a portion of the volume
control requirement. These methods include tree plantings, native grass buffers, porous pavements,
impervious disconnections, green roofs, constructed wetlands, and soil amendments.
Credit for each method is given on an area basis at the following depths:
tree plantings 0.05 inch
native grass buffers 0.05 inch
natural area preservation 0.05 inch
soil amendments 0.05 inch
impervious disconnection 0.10 inch
porous pavements 0.50 inch + not counted in impervious calculation
green roofs 1.00 inch + not counted in impervious calculation
An example of the credit reduction can be found in Section Nine, Miscellaneous and CN Reductions.
Each CN reduction method has additional requirements described in Section 9. Additional CN
reduction techniques may be proposed. Approval of such techniques and assignment of credits will
be at the discretion of the City.
Greywater/Stormwater Recycling:
For many applications, the use of pond water for irrigation can be a very cost eff ective method of
volume control. Since these systems do not directly function on a storm by storm basis an applicant
must work with the City to determine the amount of volume control credit to be applied.
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Infiltration:
If infiltration is used the following is required:
1. Requirements and recommendations laid out in the Minnesota Stormwater Manual shall be
followed.
2. Infiltration tests shall be used to provide a base infiltration rate of surrounding soils. The base
rate shall be reduced to a conservative rate for the design. The infiltration tests shall be
conducted at the location and elevation of the proposed infiltration system.
Bioretention:
If bioretention is used the following is required:
1. Requirements and recommendations laid out in the Minnesota Stormwater Manual shall be
followed.
2. Infiltration tests shall be used to provide a base infiltration rate of surrounding soils. The base
rate shall be reduced to a conservative rate for the design.
Stormwater Wetlands/Constructed Wetlands:
Constructed wetlands may be utilized to abstract volume. Since these systems do not directly
function on a storm by storm basis an applicant must work with the City to determine the amount of
volume control credit to be applied.
1. Requirements and recommendations laid out in the Minnesota Stormwater Manual shall be
followed.
Offsite Stormwater Management:
For Qualifying Small Sites, any of the above credits can be used at an offsite location to meet the
volume control requirement with the approval of the City. The offsite location must be within the same
watershed. Offsite BMPs must be permanently protected through an easement, development
agreement and/or maintenance agreement, to ensure the volume reduction feature continues to
function as designed.
For NPDES Permit Sites, offsite stormwater management may be allowed for meeting TSS and/or
TP reduction requirements [MS4 Permit, Part III.D.5.a(4)].
Stormwater Management Overlay District #2 – All Landlocked Basins
If a development is in a tributary area to a landlocked basin, the following restricted volume control is
required for that tributary area:
Volume shall be reduced in the proposed condition by a volume equal to or greater than 1.0
inches over all new impervious surfaces.
Extended duration detention is required such that volume discharging offsite in the proposed
condition not exceed the volume discharging offsite in the existing conditions in the 24 hour
period following the peak of the 100-year, 24 hour rainfall event (NRCS MSE3 rainfall
distribution).
Provision of an outlet or emergency overflow does not reduce the amount of Volume Control required.
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Stormwater Management Limitations and Exceptions:
Infiltration techniques to achieve volume control requirements are prohibited when infiltration BMPs
will receive discharges from, or are constructed in areas:
Where industrial facilities are not authorized to infiltrate industrial stormwater under an
NPDES/SDS Industrial Stormwater Permit issued by the MPCA
Where vehicle fueling and maintenance occur
With less than 3 feet of separation distance from the bottom of the infiltration system to the
elevation of seasonally saturated soils or the top of bedrock
Where high levels of contaminants in soil or groundwater will be mobilized by the infiltrating
stormwater
Infiltration techniques to achieve volume control requirements, (without higher engineering review
and City approval) sufficient to provide a functioning treatment system and prevent adverse impacts
to groundwater, are restricted when the infiltration BMPs will be constructed in areas:
With predominately Hydrologic Soil Group D (clay) soils
Within 1,000 feet up-gradient, or 100 feet down-gradient of active karst features
Within a Drinking Water Supply Management Area (DWSMA) as defined in Minn. R.
4720.5100, subp. 13
Where soil infiltration rates are more than 8.3 inches per hour
For linear projects where the lack of right-of-way precludes the installation of volume control practices
that meet the volume control requirements, and a reasonable attempt has been made to obtain right-
of-way during the project planning process, exceptions for stormwater discharge volume under the
following circumstances:
The owner and/or operator of a construction activity is precluded from infiltrating stormwater
through a designed system due to any of the infiltration-related limitations described above,
and;
The owner and/or operator of the construction activity implements, to the maximum extent
practicable, volume reduction techniques other than infiltration on the site of the original
construction activity that reduces stormwater discharge volume, but may not meet the volume
control requirements.
Wellhead protection area:
Soil infiltration features must comply with requirements and limitations of wellhead protections
plans.
Stormwater Mitigation Provisions
Stormwater mitigation provisions shall apply to all NPDES Permit Sites, as defined in this section.
Stormwater mitigation shall comply with the MS4 Permit, Part III.D.5.a(4), Mitigation Provisions (page
17 of 38).
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Long-Term Maintenance of Structural Stormwater BMPs
Structural stormwater BMPs not owned or operated by the City of Prior Lake that were implemented
to meet the conditions for post-construction stormwater management in the MS4 Permit, Part
III.D.5.a(2) shall comply with the MS4 Permit, Part III.D.5.a(5).
4.4 Low Floor / Low Opening Elevations
Low Floor Elevations and Low Opening Elevations are to be designed to the following standards:
Low floor elevations shall be at least:
3’ Above OHW or Highest Known (whichever is greater)
2’ Above HWL
Low opening elevations shall be at least:
2’ Above EOF
In the case of a landlocked basin, low floor elevations shall be at least:
3’ above the basin overflow elevation or 3’ above back to back 100-year, 24-hour rainfall
events (NRCS MSE3 rainfall distribution.
4.5 Additional Requirements
For development or redevelopment projects, the developer and/or property owner is responsible for
the removal of all significant vegetation (trees, stumps, brush, debris, etc.) from any and all areas
which would be inundated by the designated controlled outlet elevation of any required ponding areas
as well as the removal of all dead trees, vegetation, etc., to the high water level of the pond.
Upon the completion of the construction of a Structural Stormwater BMP, the developer is required
to submit an as-built record plan of the ponding area certifying that the Structural Stormwater BMP
constructed meets all design parameters. The developer may over-excavate the bottom of
stormwater ponds to compensate for erosion that will occur. The developer will be responsible for
verifying, at the end of the warranty period, that the ponds are providing the required volume.
4.6 Water Quality
The water quality treatment standard for new stormwater ponds is a 60% reduction in Total
Phosphorus (TP) and 90% reduction in Total Suspended Solids (TSS) from the proposed developed
area draining to a stormwater pond. Section Seven, Stormwater Pond Design Criteria, details
standard wet pool detention pond design criteria.
Alternatives to stormwater ponds may be proposed but must meet water quality treatment standards.
If alternatives are proposed, documentation must be submitted by the applicant based on literature
values or independent laboratory work to demonstrate the performance of the alternative being
proposed.
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SECTION FIVE:
DRAINAGE ALTERATIONS AND FLOODPLAIN MANAGMENT
5.1 Landlocked Basins
If a landlocked basin (tributary area < 25 acres) is proposed to be connected to a downstream system
the following is required:
If the landlocked basin contains a wetland, the rate of outflow from that wetland must follow
provisions for the “Alternate Rate Control Standard for Wetlands utilized for Volume
Management” detailed in Section 4.
If the landlocked basin contains a wetland, Stormwater Utilization must occur to the maximum
extent allowable under provisions for wetlands detailed in Section 6.
If the landlocked basin does not contain a wetland, or the wetland is legally proposed to be
filled under the Wetland Conservation act, the volume storage lost to connection must be
mitigated by increasing volume storage of a pond or wetland equal to the lost volume of the
landlocked basin utilized in the 100 year storm event.
All Provisions described in Section 5, Drainage Alterations must be followed.
If a landlocked basin (tributary area > 25 acres) is proposed to be connected to a downstream system
the following is required.
All requirements listed above apply.
The PLSLWD or Scott WMO must review the proposed connection. All conditions of Scott
WMO or PLSLWD approval must be met.
5.2 Drainage Alterations
If the applicant proposes to artificially drain, connect a landlocked basin, obstruct, or redirect the
natural flow of runoff the following is required:
Drainage alteration (tributary area < 5 acres) requirements:
Demonstrate:
That overall change in flow volumes to each subwatershed do not burden downstream
infrastructure.
Requirements:
Considered a minor alteration provided applicant demonstrates that downstream burdens do
not exist.
If there is evidence to suggest there is or will be a flooding problem immediately downstream
of the proposed alteration, the requirements for drainage alteration of between 5 and 25 acres
shall apply.
Drainage alteration (tributary area > 5 and < 25 acres):
All requirements listed above apply.
Demonstrate:
There is a necessity for such a change.
Reasonable care has been taken to avoid impact to upstream or downstream land.
Efforts have been taken to mitigate changes in downstream volume and rates.
Requirements:
City approval of drainage alterations is required.
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Peak rate to the gaining subwatershed of the drainage alteration must be held to rate control
standard per tributary acre included in the development.
Drainage alteration (tributary area > 25 acres) requirements:
All requirements listed above apply.
The PLSLWD or Scott WMO must approve the proposed alteration. All conditions of Scott
WMO or PLSLWD approval must be met.
5.3 Floodplain Alterations
If grading takes place within the floodplain (below the predicted 100-year flood elevation for a public
water) no net decrease in flood storage is allowed.
SECTION SIX:
WETLANDS
6.1 Procedure
The following procedure is dependent on the location of the wetland(s). Some requirements, common
to both Scott WMO and PLSLWD are listed under “both.” To determine which watershed
requirements apply to a project, applicants should contact the City early in the planning process.
Stormwater susceptibility is determined from the results of a wetland functional assessment
(Minnesota Routine Assessment, or MnRAM) to determine if a wetland is eligible for stormwater
utilization.
Both:
The applicant must submit a wetland delineation and a MnRAM wetland functional assessment; these
documents are then reviewed by the City.
If impacts are proposed to any wetland, the procedure follows the requirements of the Wetland
Conservation Act and these rules.
A wetland is given a functional classification dependent on the value for vegetative diversity
determined by MnRAM. Rankings are: Exceptional, High, Medium, and Low.
6.2 Requirements
PLSLWD:
Wetland replacement for impacts occurring within the PLSLWD must take place within the District at
a rate of 0.5:1 (New Wetland Credit per acre impacted.)
Both:
The City must review and approve of the wetland delineation and MnRAM results.
Any drainage, fill, excavation or other alteration of a public waters or wetlands is regulated by the
Wetland Conservation Act (WCA), State Statutes 103G.245 and regulations adopted hereunder. The
City is the Local Governing Unit (LGU) under these rules.
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A conservation easement is required over all buffers. Conservation easements shall be dedicated to
the PLSLWD in District areas or to the City in WMO areas.
6.3 Stormwater Susceptibility
Both:
Highly Susceptible: A wetland is considered highly susceptible if:
Forty percent or more of the wetland complex has highly susceptible wetland communities as
shown in Table 6.1 and;
Highly susceptible wetland communities have medium to exceptional floral diversity/integrity.
Moderately Susceptible: A wetland is considered moderately susceptible if:
Forty percent or more of the wetland complex has a moderately susceptible wetland
communities shown in Table 6.1 and;
Moderately susceptible wetland communities have medium to exceptional floral
diversity/integrity.
Least Susceptible: Wetlands with low floral diversity, as determined by MnRAM, were considered to
be least susceptible wetlands.
Slightly Susceptible: Wetlands that do no fall under the high, moderate or least susceptible categories
are considered slightly susceptible.
Table 6.1
Wetland Community Susceptibility to Stormwater Impacts
Highly Susceptible Wetland Communities* Moderately Susceptible Wetland
Communities*
Sedge Meadow Low Prairies Shrub-Carrs
Bogs Coniferous Swamps Alder Thickets
Coniferous Bogs Hardwood Swamps Fresh (wet) Meadows
Open Bogs Seasonally Flooded Basins Shallow Marsh
Calcareous Fens Deep Marsh
Wetland communities determined using key provided in MnRAM.
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6.4 Stormwater Utilization
Table 6.2
Stormwater Utilization
Hydroperiod
Standard
Highly
Susceptible
Moderately
Susceptible
Slightly
Susceptible
Least
Susceptible
100-year Storm
Bounce
Existing Existing + 0.5 ft Existing + 1.0 ft No Limit
Discharge Rate Existing Section 4:
Wetland
Standard (1)
Section 4:
Wetland
Standard (1)
Section 4:
Wetland
Standard (1)
1 & 2 year NRCS
event Inundation
Existing Existing + 1 Day Existing + 2 Days Existing + 7 Days
10 yr NRCS
event Inundation
Existing Existing + 7 Days Existing + 14
Days
Existing + 21
Days
(2) Outlet Control
Elevation
None: Note
OE/HWL on Map
None: Note
OE/HWL on Map
0 – 2 ft additional
storage
0 – 4 ft additional
storage
(1) Rates shall be held to the rate control requirements of Section 4, alternate rate control
standard for wetlands, unless obtaining these rates is prevented by inundation period
requirement.
(2) Outlet Control Elevation changes can be made to mitigate volume storage as required in
Section 5.
6.5 Buffer & No-Grade Zone Requirements
PLSLWD:
The following are the buffer and minimum no-grade zone requirements for each functional
classification. The tiered buffer requirement is based on a funct ional classification of; exceptional,
high, medium or low, and can be found using the results of the MnRAM vegetation assessment as
described above
Table 6.3
PLSLWD Buffer, Setback and No-Grade Matrix
Buffer
Requirement
Exceptional High Medium Low
Average Buffer
Width (ft)
30 30 30 30
Minimum Buffer
Width (ft)
20 20 20 20
Minimum No-
Grade Zone (ft)
10 10 10 10
Foundation
setback from
Buffer
20 20 20 20
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Scott WMO:
The following are the buffer and minimum no-grade zone requirements for each functional
classification. The tiered buffer requirement is based on a functional classification of; exceptional,
high, medium or low, and can be found using the results of the MnRAM vegetation assessment as
described above.
Table 6.4
Scott WMO Buffer, Setback and No-Grade Matrix
Buffer
Requirement
Exceptional High Medium Low
Average Buffer
Width (ft)
65 50 30 25
Minimum Buffer
Width (ft)
25 25 25 25
Minimum No-
Grade Zone (ft)
25 25 25 25
Foundation
setback from
wetland
35 35 35 35
Both:
Grade changes or other disturbances are not allowed in no-grade zones with the following exceptions:
Pipe outlets and associated riprap, reseeding or soil amendments, embankment and impacts
associated with an approved CIP transportation corridor, grade changes adjacent to approved WCA
impacts to wetlands, approved wetland or flood storage mitigation areas and temporary impacts
associated with utility installation.
A buffer width may vary using “Buffer Averaging.” Buffer width may be reduced to the minimum buffer
width, but the overall buffer area must be equal in area to a hypothetical fixed width average buffer
around the same wetland.
6.6 Buffer Vegetation Requirements:
Both:
Buffer must be seeded with a native mix with forbs. A two year maintenance period is required as
part of the developers agreement or other City agreement. If at the end of the two year maintenance
period the seed has not established, there is a prevalence of invasive species, or there are other
encroachments, over-seeding or reseeding may be required.
Land use within a buffer shall be subject to the following restrictions: Buffer vegetation shall not be
cropped, cultivated, hayed, mowed, fertilized, or subject to the placement of mulch or yard waste or
otherwise disturbed, except for the periodic cutting or burning that promotes the vegetative health of
the buffer or as needed to address invasive or noxious species. Buffers may be temporarily disturbed
when permitted by the City. No new structure or hard cover may be placed within a buffer area. No
fill, debris, or other material may be excavated from or placed in a buffer area.
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Buffer strips shall be required whether or not the wetland is on the same parcel as the proposed
development or on an adjacent parcel. Wetlands on adjacent parcels need not be delineated, but an
estimation using aerial photos or other methods will be required.
If acceptable vegetation is in place, reseeding is not required. Acceptable natural vegetation has the
following characteristics: A continuous dense layer of perennial grass uncultivated or unbroken for 5
years or has an overstory of trees of shrubs uncultivated or unbroken for 5 years.
6.7 Buffer Monuments and Easement:
Both:
Buffer strips shall be identified within each parcel by permanent monuments. A monument shall be
required at each parcel line where it crosses a buffer strip and shall have a maximum spacing of 200
feet along the edge of the buffer strip. An additional monument shall be placed at the midpoint of
each lot and/or as necessary to accurately define the edge of the buffer strip (considering curvature).
A monument shall consist of a post and a buffer strip sign. The signs shall comply with City Plate
#203, Wetland Boundary Signs. The signs shall be installed prior to the issuance of a Building Permit
and should be shown on the approved plans. Buffer strip signs must be purchased from the City at
a cost shown on the latest fee schedule.
All buffer strips must be covered by drainage and utility easement and conservation easements.
Drainage and utility easement shall be granted to the City of Prior Lake. Conservation easements
shall be dedicated to the PLSLWD in District areas or to the City in WMO areas.
SECTION SEVEN:
STORMWATER POND DESIGN CRITERIA
Water Quality Volume
The permanent pool volume for stormwater ponds shall be calculated using the Design Calculations
for Wet Detention Ponds by Dr. William W. Walker (1987) presented below.
WA Total Watershed area (acres)
iA Area of impervious surfaces draining to stormwater conveyors (acres)
iF Impervious Fraction
w
i
A
A
CN area weighted mean NRCS curve number for pervious portion of watershed (Based on soil
type and land cover)
P= Design storm size =2.5 (inches)
101000
CNS Maximum soil retention (inches)
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iiFSP
SPFPR
18.0
2.0 2
= Runoff for design storm (inches)
12
wARV Volume of permanent pool (acre-feet)
Rate Control Volume
The active volume (between the OE and the HWL) shall be sized to meet the rate control requirements
outlined in Section 4, Rate Control, using a maximum slope at 4:1 (H:V).
Additional Design Criteria
The use of regional ponding, stormwater wetlands, or expandable ponding is encouraged by the City.
A 10’ wide aquatic vegetation bench is required below the OE of the pond, with the maximum slope
of 10:1.
The invert elevations of pond inlet flared end sections shall match the OE of the pond. Submerged
outlets will only be allowed at the discretion of the City.
Outlet control structures from ponding areas are required as directed by the City. Location and
appearance of outlet structures shall be subject to City approval and may require landscape
screening.
The EOF of a pond should be at least 1 foot higher than the HWL. The top of dike elevation should
be at least 2 feet higher than the HWL.
Dikes used to create rate control ponds must at maximum use 4:1 slopes and measure 10 ’ wide at
top. At minimum, a clay core should be designed in consideration of groundwater flow. If head
difference between OE of pond and downstream land exceeds 3’, soils data will be required in the
area and dike design must address maintenance of pond water level and dike stability. Outlet pipes
through engineered dikes with head differences greater than 6’ should be designed with anti-seep
collars. Sand bedding shall not be used through dike section.
Pond outlets shall provide floatable debris skimming for the 10-year, 24-hour rainfall event (NRCS
MSE3 rainfall distribution). A manhole with a baffle wall with orifice or notch is recommended to
control rate. Outlet rate control manholes shall have a top mitered to conform to fill. A 66” minimum
diameter is required to provide access to both sides of the weir wall.
SECTION EIGHT:
STORM SEWER DESIGN CRITERIA
Storm sewer facilities shall use design criteria utilizing a rational or hydrograph method based on
sound hydrologic theory to analyze the storm water runoff and proposed development. (Such as the
Soil Conservation Service TR-55 Urban Hydrology for Small Watersheds)
Storm sewer facilities shall be designed for a 10-year, 24-hour rainfall event (NRCS MSE3 rainfall
distribution) for local pipe design and a 100-year, 24-hour rainfall event (NRCS MSE3 rainfall
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
18
distribution) for ponding detention basin design and trunk facilities. Pipe size and grade shall be
greater than 15” ID and 0.5% slope. Pipe class shall conform to design standards as shown in
“EXHIBIT M”.
Drainage calculations shall be submitted to show the sizing of pipe, ponds, emergency overflow
spillways, and catch basin interception analysis. Assuming catch basins can receive a maximum of
3 cfs, multiple catch basins may be required at low points.
Provide for overflow routes to drain all street and backyard low points.
SECTION NINE:
MISCELLANEOUS AND CN REDUCTIONS
Section 4 detailed a credit system used for volume management; the following is additional
information on that credit system.
The following calculation is an example of volume control met entirely through the use of CN
reductions. This will not be suitable for most sites but serves as an example on how to use a variety
of methods to meet the requirement.
50 acre site with 20% impervious surfaces, = 10 acres new impervious (actual calculation required)
10 acres impervious x 0.5in volume control requirement = 5ac-in or 18150cf volume.
(see next page for sample calculation)
Volume Credits Claimed:
CN Reduction Category Area (acres) Area basis depth (in) Credit (ac-in)
Native grass buffers 5 0.05 0.25
Pervious pavers 1 0.50 0.50
Pervious paver area no longer
counted in impervious calculation
1 0.50 0.50
Tree plantings 5 0.05 0.25
Soil amendments 30 0.05 1.50
Impervious area disconnection 5 0.10 0.50
Green roof 1 1.00 1.00
Green roof area no longer counted
in impervious calculation
1 0.50 0.50
Total Volume Credits: 5.00 ac-in
Additional Requirements for CN Reduction
Tree plantings:
Area determinations for tree plantings shall be assumed at 500sf per tree. (Based on an conservative
average water use of 1cf per day per tree at 7 years in an open canopy condition, less average tree
mortality, 3days water use per storm 0.7*(1/(.05/12))*3 the beneficial effects of canopy intercept are
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
19
ignored). This reduction can be used in combination with the native grass buffer (ex. Oak prairie
restoration could count as tree planting, native grass and soil amendment reduction).
Native grass buffers:
Area determination shall only include buffers currently, or proposed to be, established in a native
species. Area must be included in a permanent conservation easement dedicated to the City or
PLSLWD.
Natural area preservation:
Upland wooded or prairie areas proposed include only those areas not already prohibited from
development (buffers, bluffs, etc.) and must be kept in their natural state through outlot dedication
and/or conservation easements. No grading is allowed in preservation areas. Preservation area
must be denoted through the use of decorative fencing, informational signing, or other methods
approved by the City.
Soil amendments:
Soil amendments must take place after building construction is compete to avoid compaction during
the construction process.
Soil amendment shall be designed to mitigate the effects of compaction due to mass grading by
returning the soil to a loose, friable state able to transmit water.
All soil amendments must be designed by a licensed professional engineer or professional soil
scientist. Soil design must promote deep loosening of the mass-graded soils strata, and improvement
of infiltration and moisture retention characteristics of the topsoil. (Example: 18” deep ripping or tilling
of base soils and compost mix after mass grading, followed by the application of a designed mix of
compost, peat, sand, and topsoil and spread at 6” depth).
Impervious disconnection:
Area determination for impervious disconnections will be that roof area or select pavement area that
is disconnected from the drainage system and allowed to flow over natural grounds that are designed
to promote infiltration and transpiration. Design shall not cause wet lawn conditions, basement
seepage, or other nuisances. Design must discourage reconnection to impervious surfaces by
providing a minimum of a 75’ pervious flow path.
Porous pavements:
Area determination for porous pavements will be only that area meeting the following requirements:
Porous pavement systems must use permeable base material and promote infiltration. Porous
pavements must be designed by a licensed professional engineer and approved by the City.
Green roofs:
Area determination for green roofs will be only that area meeting the following requirements: Design
must be must be designed by a professional architect and meet Building Code. The design must be
approved by the City.
City of Prior Lake
Public Works Design Manual
Adopted July 16, 2007
20
More information on these and other CN reductions and site design measures can be found in the
MPCA stormwater manual.
“EXHIBIT L”
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CHECKLIST 1.doc
RESIDENTIAL BUILDING PERMIT CHECKLIST
ENGINEERING DEPARTMENT REQUIREMENTS
EROSION & SEDIMENT CONTROL
Silt fencePerimeter sediment control (silt fence, compost logs, etc.)
Rock construction entrance
Erosion control (straw mulch, blanket, etc.)
Special erosion control measures if needed
GRADING
Water conveyance to drainage & utility easements
Driveway slope
Contours
Compare development grading plan
BUILDING CLASSIFICATION
Match style against development grading plan
Driveway location versus per grading plan
Check low floor versus grading plan and wetland high water level
Verify building location to make sure it is on the building pad
“EXHIBIT L”
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CHECKLIST 1.doc
FINAL GRADE INSPECTION CHECKLIST
Curb box elevation and accessibility
Water conveyance
Slopes (3:1 or 4:1)
Visual swale between properties
Driveway width – 24 foot width maximum at curb to right-of-way
Ford A-1 cover for water shut off valves in driveways
Check concrete sidewalk and curb for damage
Concrete driveway apron between curb and sidewalk
Erosion & sediment control
Wetland buffer not infringed upon or re-graded
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SWPPP Template for
Small Construction Sites
Stormwater Pollution Prevention Plan (SWPPP)
Doc Type: Stormwater Pollution Prevention Plan
Instructions: This Stormwater Pollution Prevention Plan (SWPPP) Template is intended to provide a means for small (three acres or
less) construction sites to comply with the General Stormwater Permit for Construction Activity. Before completing this SWPPP, you
must read and understand the requirements in the Minnesota General Stormwater Permit for Construction Activity (MN R100001)
available from Minnesota Pollution Control Agency (MPCA) website at http://www.pca.state.mn.us/water/stormwater/index.html. A list
of the SWPPP requirements can be found at http://www.pca.state.mn.us/index.php/view-document.html?gid=7423. This template will
help you complete the SWPPP components required in Part III and IV of the permit. Persons preparing SWPPPs are required to
have had training in preparation of SWPPPs (Part III.F.). [Note: To check the checkboxes, ‘double click’ the box and select
“checked” and select “okay”.]
I. General Construction Activity Information
a. Project name:
b. Describe the construction project location (address/city or township/county/latitude/longitude):
Address or describe area:
City or Township: State: MN Zip code:
Latitude/Longitude of approximate centroid of project:
c. Describe the construction activity (type of construction, phases, timelines, potential for discharge of sediment
and other pollutants, etc.):
Project type: (To check the checkboxes, ‘double click’ the box and select “checked” and select “okay”.)
Residential Commercial/Industrial Road construction
Residential and road construction Other (describe):
d. Number total of acres to be disturbed: (tenths of an acre)
e. Pre-construction acres of impervious surface: (tenths of an acre)
f. Post-construction acres of impervious surface: (tenths of an acre)
g. Total new impervious surface acres: (tenths of an acre)
(Examples of impervious surface include rooftops, sidewalks, patios, driveways, parking lots, storage areas, and concrete, asphalt, or
gravel roads.)
II. Receiving Waters
a. List all waters within one mile (nearest straight line distance) that are likely to receive stormwater runoff from
the project site both during or after construction:
Receiving waters within one mile of project property edge:
Water body ID* Name of water body
Type
(ditch, pond, wetland,
calcareous fen, lake,
stream, river)
Special water?
(See Stormwater Permit
Appendix A)
Impaired Water?**
(See Stormwater Permit
Appendix A)
Yes No Yes No
Yes No Yes No
Yes No Yes No
Yes No Yes No
* Water Body identification (ID) might not be available for all water bodies. Use the Special and Impaired Waters Search Tool at:
http://www.pca.state.mn.us/water/stormwater/stormwater-c.html.
** Impaired water for the following pollutant(s) or stressor(s): phosphorus, turbidity, dissolved oxygen, or biotic impairment.
EXHIBIT O
ATTACHMENT 5
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b. Use the Special and Impaired Waters Search Tool to locate special and impaired waters at
http://www.pca.state.mn.us/wfhya5b).
c. Incorporate into this SWPPP any additional Best Management Practices (BMPs) or other specific construction
related implementation activities identified in an approved Total Maximum Daily Load and Waste Load
Allocations.
d. Identify adjacent public waters where the Minnesota Department of Natural Resources (DNR) has declared
“work in water restrictions” during fish spawning timeframes:
e. Attach maps (U.S. Geologic Survey 7.5 minute quadrangle, National Wetland Inventory maps or equivalent)
showing the location and type of all receiving waters, including wetlands, drainage ditches, stormwater ponds
or basins, etc. that will receive runoff from the project. Use arrows showing the direction of flow and distance to
the water body.
f. Identify wetland impacts:
1. Will construction result in any potential adverse impacts to wetlands, including excavation, deg radation of water
quality, draining, filling, permanent inundation or flooding, conversion to a stormwater pond? Yes No
2. If yes, describe impacts and mitigation measures that were taken to address the impacts (in accordance with Part D
of Appendix A of the permit) and attach to this SWPPP, copies of permits or approvals from an official state wide
wetland program issued specifically for this project or site:
g. Describe any stormwater mitigation measures that will be implemented, as a result of an environmental review,
endangered or threatened species review or archeological site review:
h. Describe any additional (or different) stormwater management measures required for karst or drinking water
supply management areas to protect groundwater standards:
III. Project Plans and Specifications
a. Attach to this SWPPP site maps and/or plan sheets that depict the following features:
The project location and construction limits.
Existing and final grades, including dividing lines and direction of flow for all pre and post-construction
stormwater runoff drainage areas located within the project limits.
Soil types at the site.
Locations of impervious surfaces.
Locations of areas not to be disturbed (e.g., buffer zones, wetlands, etc.).
Steep slope locations.
Locations of areas where construction will be phased to minimize duration of exposed soils.
Portions of the site that drain to a public water with DNR work in water restrictions for fish spawning timeframes.
Locations of all temporary and permanent erosion and sediment control BMPs as required in Part III. C & D.
and Part IV of the permit.
Buffer zones as required in Part IV.C.9 or Appendix A, Part C.3. of the permit.
Locations of potential pollution-generating activities identified in Part IV. F. of the permit.
Standard details for erosion and sediment control BMPs to be installed at the site.
b. List all anticipated erosion prevention and sediment control BMP quantities needed for the life of the project
(e.g., linear ft. silt fence, square feet erosion blanket, tons mulch, etc.):
IV. Temporary Erosion Prevention Practices
a. Describe the types of temporary erosion prevention BMPs expected to be implemented on this site during
construction:
1. Methods of temporarily stabilizing soils and soil stockpiles (e.g., mulches, hydraulic tackifiers, erosion
blankets, etc.):
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2. Methods of dissipating velocity along stormwater conveyance channels and at channel outlets (e.g., check
dams, sediment traps, rip rap, etc.):
3. Methods to be used for stabilization of ditch and swale wetted perimeters (Note that mulch, hydraulic soil
tackifiers, hydromulches, etc. are not acceptable soil stabilization methods for any part of a drainage ditch
or swale):
4. Methods to be used for energy dissipation at pipe outlets (e.g., rip rap, splash pads, gabions, etc.):
5. Methods to be used to promote infiltration and sediment removal on the site prior to offsite discharge,
unless infeasible (e.g., direct stormwater flow to vegetated areas):
b. Describe timelines to be implemented at this site for completing the installation of the erosion prevention BMPs
listed in i, ii, iii, and iv. (see Part IV. B. of the permit for minimum requirements). If applicable, include the
timeline for completing soil stabilization for areas within 200 feet of a public water with work in water
restrictions due to fish spawning time frames (Part IV.B.2.) and soil stabilization timelines for portions of the site
that drain to special or impaired waters as required in Appendix A Part C. 1.a.:
c. Describe additional erosion prevention measures that will be implemented at the site during construction (e.g.,
construction phasing, minimizing soil disturbance, vegetative buffers, horizontal slope grading, slope
draining/terracing, etc.):
d. If applicable, include additional requirements in Appendix A Part C.3 regarding maintaining a 100-foot buffer
zone or installing redundant BMPs for portions of the site that drain to special waters:
e. If applicable, describe additional erosion prevention BMPs to be implemented at the site to protect planned
infiltration areas:
V. Temporary Sediment Control Practices
a. Describe the methods of sediment control BMPs to be implemented at this site during construction to minimize
sediment impacts to surface waters, including curb and gutter systems:
1. Methods to be used for down gradient perimeter control:
2. Methods to be used to contain soil stockpiles:
3. Methods to be used for storm drain inlet protection:
4. Methods to minimize vehicle tracking at construction exits and street sweeping activities:
5. If applicable, additional sediment controls (e.g., diversion berms) to be installed to keep runoff away from
planned infiltration areas when excavated prior to final stabilization of the contributing drainage area:
6. Describe methods to be used to minimize soil compaction and preserve top soil (unless infeasible) at this
site:
7. Describe plans to preserve a 50-foot natural buffer between the project’s soil disturbance and a surface
water or plans for redundant sediment controls if a buffer is infeasible:
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8. Describe plans for use of sedimentation treatment chemicals (e.g., polymers, flocculants, etc.) see Part
IV.C.10 of the permit:
b. Is the project required to install a temporary sediment basin due to 10 or more acres draining to a common
location or 5 acres or more if the site is within 1 mile of a special or impaired water? Yes No
If yes, describe (or attach plans ) showing how the basin will be designed and constructed in accordance with
Part III.C of the permit.
c. Will the project include dewatering, basin draining? Yes No
If yes, describe measures to be used to treat/dispose of turbid or sediment-laden water and method to prevent
erosion or scour of discharge points (see Part IV. D of the permit):
d. Will the project include use of filters for backwash water? Yes No
If yes, describe how filter backwash water will be managed on the site or properly disposed (see Part III.D.3. of
the permit):
VI. Permanent Stormwater Management System
a. Will the project result in one acre or more of new impervious surfaces or result in one acre or more of new
impervious in total if the project is part of a larger plan of development? Yes No
b. If yes, a water quality volume of one inch of runoff from the cumulative new impervious surfaces must be
retained on site (see Part III.D of the permit) through infiltration unless prohibited due to one of the reasons in
Part III.D.1.j. If infiltration is prohibited identify other method of other volume reduction (e.g., filtration system,
wet sedimentation basin, regional ponding or equivalent method:
c. Attach design parameters (see Part III.D.) for the planned permanent stormwater management syst em, including
volume calculations, discharge rate calculation, construction details including basin depth, outlet
configurations, location, design of pre-treatment devices and timing for installation. For more design
information consult the Minnesota Stormwater Manual on the MPCA website at
http://stormwater.pca.state.mn.us/index.php/Main_Page.
d. For infiltration systems attach on site soil testing results verifying soil type and distance to the seasonal water
table or bedrock (from bottom of the basin) in the location of the infiltration or filtration system.
e. For linear projects with lack of right of way to install treatment systems capable of treating the entire water
quality volume, identify other method(s) for providing treatment of runoff prior to discharge to surface waters
(e.g., grassed swales, filtration systems, smaller ponds or grit chambers, etc.):
1. Attach to this SWPPP documentation of reasonable attempts made to obtain right o f way for stormwater
treatment systems.
f. For projects that discharge to trout streams, including tributaries to trout streams, identify method of
incorporating temperature controls into the permanent stormwater management system:
VII. Inspection and Maintenance Activities
a. Identify the trained individual(s) responsible for installing, supervising, repairing, inspecting , and maintaining
erosion prevention and sediment control BMPs at the site:
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b. Attach training documentation for each individual:
c. Describe procedures to routinely inspect the construction site, including:
1. A description of record-keeping requirements and content (see Part IV.2. of the permit):
2. Frequency of inspections (see Part IV.E.1. and 3 of the permit.):
3. Areas to be inspected and maintained (see Part IV.E.5. and 6. of the permit):
VIII. Pollution Prevention Management Measures
a. Describe practices for storage of building products with a potential to leach pollutants to minimize exposure to
stormwater:
b. Describe practices for storage of pesticides, herbicides, insecticides, fertilizers, treatment chemical, and
landscape materials:
c. Describe practices for storage and disposal of hazardous materials or toxic waste (e.g., oil, fuel, hydraulic
fluids, paint solvents, petroleum-based products, wood preservative, additives, curing compounds, and acids)
according to Minn. R. ch. 7045, including restricted access and secondary containment:
d. Describe collection, storage and disposal of solid waste in compliance with Minn. R. ch. 7035:
e. Describe management of portable toilets to prevent tipping and disposal of sanitary wastes in accordance with
Minn. R. ch. 7040:
f. Describe spill prevention and response for fueling and equipment or vehicle maintenance:
g. Describe containment and disposal of vehicle and equipment wash water and prohibiting engine degreasing on
the site:
h. Describe storage and disposal of concrete and other washout wastes so that wastes do not contact the ground:
IX. Final Stabilization
a. Describe method of final stabilization (permanent cover) of all disturbed areas:
b. Describe procedures for completing final stabilization and terminating permit coverage (see Part IV.G.1-5):
Documentation of infeasibility:
“EXHIBIT Q”
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PROTOCOL FOR THE ADMINISTRATION OF THE
WETLAND CONSERVATION ACT (WCA)
I. WETLAND DELINEATION SUBMITTAL
a. The applicant will need to submit a completed report for our review, including a site
location map, a map of the wetland boundary, data sheets describing the sample
plots, maps of the soils, NWI and PWI, and a description of the existing and
proposed land use.
b. Any review of wetland delineations will only be performed within the growing
season. This will typically be between May 15th and October 15th unless special
dispensation is granted by the City.
c. In order to update and maintain the GIS database, it is requested that with all
delineation reports being submitted for review, an electronically recorded file of the
wetland boundary (in AutoCAD™ or ArcMap™ on Scott County coordinates) and
an electronic copy (in PDF) of the wetland report be submitted to the city.
d. City staff will review the submittal to ascertain that payment assurances are
considered.
e. The city will send the report to the city wetland expert for review.
i. The review must be completed within sixty days from the time of receipt
of a completed wetland report at the city offices.
ii. Upon completion of the review, the city wetland expert will notice the
decision on the jurisdictional determination within ten days per WCA
rules.
iii. A memo Notice of Application will be sent by the city wetland expert to
the consultant/land owner.
1. If there is a disagreement with the boundary, the city wetland expert
will request additional materials to support the current delineation
or an agreement to wetland boundary will be determined by the city
wetland expert and the consultant.
2. If no disagreement is found then a memo Notice of Decision stating
concurrence with the delineated wetland boundary(s) will be sent,
by the city wetland expert, to the consultant/landowner and copied
to the city.
II. SUBMITTAL OF JOINT NOTIFICATION OF WETLAND REPLACEMENT PLAN
APPLICATION
a. After receiving the application, the city wetland expert will review the application
within ten fifteen business days (per WCA) to determine if the application is
complete. (NOTE: It is the responsibility of the applicant and/or their agent
to assure that all Technical Evaluation Panel (TEP) members receive a copy
of the application.)
“EXHIBIT Q”
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i. If complete, the city wetland expert will send WCA Notice of Completed
Application submittal to Technical Evaluation Panel (TEP) members
including the applicant.
ii. If incomplete, the city wetland expert will send letter a request to applicant
stating reason(s) for such a determination and request these materials
be supplied.
b. Once the application submittal is determined to be complete, there will be a 15 to
30 day comment period. This will typically be 30 days unless the City specifically
requests otherwise. The ending date of the comment period will be stated in the
Notice of Application.
c. A Technical Evaluation Panel (TEP) will typically be held within the comment
period and occasionally afterwards. If it happens that the application is
straightforward and simple, a TEP may not be held. The city wetland expert will
coordinate the scheduling of the TEP.
i. The TEP members will review and comment on the application.
ii. The minutes of the TEP and the TEP Findings of Fact will be drafted by the
city wetland expert for review, approval and signing. Once reviewed, the
city wetland expert will obtain signatures from the other TEP members.
III. REPLACEMENT PLAN APPLICATION DECISION
a. Should the TEP deny the plan or request additional information, the applicant will
amend their application and resubmit to the TEP for review. (See item 2)
b. Should the TEP agree to the replacement plan, a Notice of Decision and cover
memorandum will be sent to the city for final review and to be placed on the next
available City Council meeting.
c. The Council will decide whether they agree with staff recommendation and
approve the replacement plan or if they will deny the application.
i. If approved, the city wetland expert will sign the notice and send to the
applicant and all TEP members. (NOTE: If approved, an electronic
file of the wetland boundary, any wetland impacts and any newly
created wetland mitigation areas should be submitted to the city.
These should be in either AutoCAD™ or ArcMap™ and they should
be on Scott County coordinates.)
ii. If denied, the applicant will need to comply with council recommendations
or resubmit the application.
IV. WETLAND EXEMPTIONS
a. Applications for wetland exemptions will be reviewed by the city wetland expert. If
an exemption is granted, it will be handled administratively. In the event that an
exemption is denied, the exemption will be presented to the council for action.
b. Projects with known wetland resources but no direct impacts should be reviewed
to determine that No Net Loss will occur as a result of the proposed activities.
“EXHIBIT Q”
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Some examples might include secondary impacts due to watershed diversion or
inadequate erosion control measures.
V. WETLAND MONITORING
a. Minnesota Rules Chapter 8420 state that a five year monitoring plan must be
developed and implemented for all wetland mitigation accomplished through the
creation of wetland areas.
b. The monitoring can be accomplished through either of the following:
i. The applicant can develop and submit a monitoring plan to the TEP for
their review and approval.
1. The plan must include who is responsible for the monitoring. An
annual monitoring report, consistent with MN Rules 8420 must be
submitted to the City of Prior Lake for review. Monitoring will end
after the mitigation is determined to be successful.
2. In the event that this exceeds the five year monitoring plan, the city
wetland expert will inform the applicant in writing that the monitoring
period is being extended and the rationale for the extension.
3. An as-built of the monitoring area must be supplied to the City
electronically in either AutoCAD™ or ArcMap™ on Scott County
coordinate.
4. The city wetland expert will review the monitoring report for
accuracy and filed field check the site.
ii. The applicant may defer the monitoring to the City of Prior Lake.
1. Assurance monies will need to be deposited into an escrow account
to cover the cost of monitoring.
2. The city wetland expert will monitor the mitigation areas on behalf
of the city for the five year period or until the area has been
determined successful as per item V.b.i above.
3. The city wetland expert will use GPS equipment to as-built the area
of mitigation.
VI. OTHER PERMITS/APPROVALS
a. Approval of wetland boundaries or project impacts under the Wetland
Conservation Act does not preclude the need for the applicant to obtain approvals
from other regulatory agencies, including but not limited to:
City of Prior Lake
US Army Corps of Engineers
Department of Natural Resources
Watershed District(s)
Minnesota Pollution Control Agency
E a g l e
C r e e k
LowerPriorLake
PikeLake
MysticLake
HaasLake
UpperPriorLake
ArcticLake
JeffersPond
HowardLake
City of Prior Lake
Last Updated June 2016City of Prior Lake GIS Department
STORMWATERMANAGEMENTOVERLAY DISTR ICT #1PRIOR LAKE OUTLETCHANNEL
Minnesota2016 ²
City Limits
Subwatershed Boundary
SW Management Overlay District
0 0.25 0.5
Miles
FIGUR E 2
LowerPrior Lake
MysticLake
HaasLake
UpperPriorLake
SpringLake
ClearyLake
RiceLake
O'DowdLake
HowardLake
456712
456744
456716
456718
456717
456782
456742 456742
456721
456723 456787
456727
456717
456714
456778
456783
456781
456721
PARK VIEWCIR
CARDINALRIDGE T RL
OV ERLOOK CIR
TURNERDR
JEFFERS CT
OMEGA DR
FOOTHIL L T RL
140 ST
DEWITTEAVE
PRIVATE PENNSYLVANIAAV
WAT ERFALL CT
PONDSWAY
HER O N C T
SEAGULLCIR
HAMP TONST
WILDS DR
MALCOLM CT
WILDERNESSCIR
ZINRANCT
WREN CT
TWIN PONDSCURVE
MISSIONTRL
CEDARCIR
COA CHMANLN
FOX TRL
W ILLO W W O O DCIR
WESTVIRGINIA CT
STORMSCIR
WOODRIDGECT
MARKLEYLAKE CT
BOBCATCIR
EAUCLAIRECIR TERRICIR
WELLINGTONCT
HORIZON DR
HUMMINGBIRDCT
MUL BERRY CIR
WILDERNESSCT
CREEKVIEWCIR
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21 AV
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174 ST
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135 ST
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MEA DOWAV
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GATE WAY ST
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-A13-A282
-A13
City of Prior Lake
Last Updated June 2016City of Prior Lake GIS Department
WATERSHED DISTRICT& WMO BOUNDA RY
Minnesota2016 ²
CITY BOUN DARY
PL/SL WATERSHED DISTRICT
SCOTT WM O
STATE HIGH WAY
COUN TY R OAD/HIGHWAY
PUBLIC ST REET
PRIVATE STREET
0 0.25 0.5
Miles
FIGUR E 2